Hello and welcome to my User Tip
This tip is designed to act as a methodical catch all, step by step guide to resolving unknown issues for 10.6-10.7 users.
None of the steps will hurt your machine or have a effect on the other steps, if followed as intended and it increases in complexity the further it progresses.
STOP if you feel anything is overwhelming you and seek professional assistance.
STOP and report back to your original thread any kind of warning or irregular behavior any of these steps give.
STOP if the procedure has resolved your issue obviously...duh.
I will give adequate notice if any of the steps may possibly or will delete your data.
Please report back what steps you have completed to your original thread so we can assist further.
Also any machine specs, your OS X version, software installed, etc etc so we can visualize your machine as we can't see it.
If your using a wireless keyboard, you need to use a built in or wired USB keyboard (no hubs) to execute the "hold this key or that key" boot key commands.
Obviously if a firmware password has been applied the boot key commands won't work.
Also disconnect all non-related hardware, like external drives, monitors etc. Port powered drives may need a powered USB hub.
1. SMC Reset https://support.apple.com/kb/HT3964
If the battery is not charged (from like letting it sleep too long), let the Mac charge up awhile first.
3. Hold Option key boot (Startup Manager) and select your OSX boot drive, once in select the Startup Disk and your OS X drive.
This is usually for "Flashing question mark"" or if you have Windows in Bootcamp and it doesn't boot back into OS X
If this doesn't solve your issue, could be the drive is corrupted, dead or the Mac is having hardware issues.
4. Hold Shift key boot (Safe Mode) and restart normally again https://support.apple.com/kb/HT1455
You will see a progress bar go across the screen, if it completes your good and you reboot and everything is fine, then good. Stop.
If your machine only operates in Safe Mode: then #5, 12, 13, 16 (or even 18 or 19) likely apply to you.
If you see the progress bar each time you boot, you need to continue,
5: Not booting up still?
6. Drag and Drop to copy
your Users file folders off the machine to a external storage drive (no TimeMachine setups now) and disconnect all drives.
If you have a TimeMachine drive or clone backup, do this step regardless because either or both of those could be corrupted.
If you can't do this now, the first opportunity you do, do this step, saving your Users data is priority #1 a all times.
If you don't know what a storage drive is or don't have a backup, then read this thread about backups.
This link is for if you can't boot and need to copy, delete or "undelete" data from the drive
7. Software Update fully under the Apple Menu
Then reset your router, disconnect your network/Internet and reboot. Test.
Is the problem a network issue or not?
If so, then check for network related issues, reset your router etc.
I have some possible fixes here
Some of the tips below may actually assist in fixing so continue.
6: Disk Utility > Repair Permissions from the Utility folder
Select your drive on the left, click First Aid, then click Repair Permissions.
You can choose to Repair Disk, but if it gives any error or "drive can't be unmounted" etc you need to proceed to next step. #7 as that is more reliable method to Repair the drive and advised.
If you see it giving the same list of permissions fixed, "Warning SUID file changed and won't be repaired" type messages can be safely ignored.
7: Disk Utility > Repair Disk
10.6 users - hold c and boot from the 10.6 installer disk, select the drive or parittion on the left, Repair Disk & Permisisons.
10.7+ users - hold command r boot from Lion Recovery HD, select the drive or parittion on the left, Repair Disk & Permisisons.
If DU repaires the drive, run it again to make sure.
See if that cures your problem, sometimes there are two or more problems and this step only cured one of them, so keep going to #8.
If DU gives a error and can't repair the drive, you have a more serious drive issue.
8: Hardware Test https://support.apple.com/kb/ht1509
If it gives anything, write it down and consider taking it in for service.
9: Reset User's Permissions
On 10.6, hold c or option key boot off the 10.6 disk and use the Password Reset under the Utilities menu.
For 10.7 Lion follow these steps:
Hold down the Command and R keys while booting.
Select Terminal in the Utilities, Type resetpassword and hit Return.
Don't reset if your Repairing Users Permissions, instead click on icon for your Mac’s hard drive at the top. Select the user account where you're having issues.
You'll see an area labeled Reset Home Directory Permissions and ACLs. Click the button.
10: OnyX cache cleaning
This routine cleans all possible corrupt caches, doesn't delete your data or programs.
If any of the initial checks OnyX does gives a warning, then Stop and report, you have a serious drive or other issue.
Sometimes a corrupted cache file can cause strange behavior, slow machine, Dock and fonts, doesn't work, beachballs effect, just general strangeness that can't be explained. Web browsing slow when all the other machines are fast etc.,
Use the free OnyX matching your OS X version and run all the initial checks
Run all the maintenance and cleaning aspects (except don't delete the log files) and reboot at the end (must)
This will give OS X a enema of sorts (won't delete file or programs) and let it rebuild all the cache and other files, including Spotlight.
OnyX also has a Verify > Preferences
(plist) file checker, show the corrupt ones and write them down. So while your in OnyX cleaning your caches, check for corrupted plist files too.
11: Corupt Preferences files
Preference files are basically that, they store your user preferences for that particular program inside the Users/Library folder (now hidden your protection in 10.7+)
If the program launches and doesn't work, or doesn't save the changes you made in it's preferences, then likely it's corresponding .plist file is corrupted.
It's a easy fix, find it, delete it, reboot and launch the program, it recreates it's own again automatically.
They are usually located in the: (use Finder: Go menu > Go to folder) /Library/Preferences
Trash the corresponding .plist file manually, reboot and relaunch the problem program again and reset preferences.
On 10.7 there may be two copies of the same .plist file, one is the original lock file and can not/should not be deleted. Delete the other that you can easily drag out to the Trash.
You don't have to perform routine maintenance on a Mac, it does it all by itself, consider this OnyX routine a "nuke the caches" and find the bad plist file sort of troubleshooting and repair step in resolving your issue.
12: Check your Console Logs and Activity Monitor
...for anything "kernel protection failure" or alerts to what is causing your problems. It's located in your Utilities folder or use Spotlight (hold command space bar) to search for it and open it. Some of these log files can only be seen in a Admin account.
Activity Monitor is located in your Utilities folder, it has the ability to see what's going on, choose the "All Processes" make a note of anything consuming a lot of CPU cycles, you can try force quitting the process, or perhaps rebooting the machine will stop it. It will give a idea of something is amiss and can assist in narrowing down your problem.
Also check Disk Usage, your drive should be less than 85% filled or you'll have issues, see Storage Drive
13: Check, uninstall, reinstall and update all your installed third party software
Including any third party system preference panes, plug-ins menu items etc for updates. Uninstall or Reinstall (using their installer/uninstaller) all third party software, install one at a time and test to find the culprit.
Browser plug-in check:
By now you know about Shift key (Safe Boot) to get you into the machine in case something you installed doesn't work and you get Gray screen issue when booting.
The Console log files can assist greatly which programs are having trouble.
Safari can be installed from Apple's web site. If the installer says "You have a newer version" then just delete the installer and either wait for Apple to update the main site (use another browser in the meanwhile) or you can proceed.
Apple bundled programs can be reinstalled along with a #16 Reinstall Just OS X method.
14: Create a new User Account
This is for determining if the problem is in located within the one User account or not or OS X itself (+ bundled programs from Apple.)
You have checked all your third party software and cleared that, it might be a corrupt program or something else that
Create a new Admin account in your System Preferences. Log into that new user and test, same problems? Used the same files? Not a file issue? Is it a particular program now working fine in this user?
Programs can store it's specific User attributes in the User account and these can become corrupted even if you reinstall the program.
So uninstall the program and it's associated user files, then reinstall it again.
Sometimes it's a file problem, you'll have to do a tedious process of elimination to find the culprit, like a corrupt picture in a huge iPhoto Library. or a song in a large iTunes Music folder.
Not So Easy
Consult on the forums about your issue before proceeding here on, it might be unnecessary or another issue altogether.
I've cobbled together some possible information not included on this User TIp here:
Ask questions on the forums the following procedures will resolve your issue or not. You'll get a good idea if so by this time and then can come back.
Please mention you have done the steps above and the results so others can grasp where and what you have done to this point.
15: Delete and Recreate the Problematic User Account
Warning: Deleting the problematic user account will destroy any data in that user account.
If you don't have a copy of the files (like you can't log into it), you need to consider the Data Recovery Step here first before proceeding.
If your problem doesn't exist in the second User account and you can't resolve it manually in the problematic account, the issue is localized the first User account, likely a bad file or Library.
If you want to save web browser bookmarks, you should try to export those first while in that problematic user account if possible.
If your problem is localized to the one user account. likely in the Users/Library folder (which is now hidden in 10.7+), you can try restoring this folder from TimeMachine or backup.
Create another Admin account, copy files out of the problem user, delete the old account, reboot and re-create the old named account and return files, thus recreating the User/Library folder devoid of corruption and settings
Sometimes the problematic user account can't be logged into, thus use the second Admin account to access the other and transfer files out.
If you have only one Admin account on the machine and can't log into it, there are ways to create another Admin account via Single User Mode (root, dangerous) via the command line. It's a advanced step, so ask on the forums or in your thread as to receive guidance in it's procedure for your OS X version.
16. Reinstall Just OS X
OS X 10.6+ has the ability to reinstall right over itself, this is helpful for kicking out anything in OS X or problematic third party kext files, giving a clean copy of OS X. Doesn't touch users or most programs, will kick out anything "non-Apple" out of OS X.
Warning: Possible user data destruction with this method, but I haven't heard of it happening, one must have a serious drive issue most likely for this to occur. Just to be safe you should consider this link if you dont' have a recent copy of your files off the machine.
OS X and bundled Apple programs are replaced. You need to Software Update fully right away after this procedure is undertaken to get OS X and bundled programs up to date with your files.
Also you will find out some software is no longer working, check for issues others are having and reinstall these non-working third party softwares one at a time until your problem (if it does) returns.
If it does and you can't boot, hold the Shift Key down (Safe Mode), that will disable it and then perform a update or remove the problematic software and notify the developer.
Use the "Reinstall Just OS X" method, not the "Erase and Install OS X"
17: Data Recovery efforts
Used if you don't have a recent copy of your files off the drive, like it's not booting, or it's been reformatted, or files accidentally deleted, file structure of the drive is not functioning etc.
18: Zero Erase and Fresh install OS X
Warning: permanent data destruction on the entire drive or partition selected. No recovery possible.
Wipes everything method. Everything erased, the hard drive bad sectors mapped off, everything new except files from storage drive, no clone or TM restores unless you know it's not corrupted.
For secure deletion for the paranoid read this:
19: Replace the hard drive
if allowed for your machine, reinstall the OS and everything.
Only should do if you're out of AppleCare/ warranty or for security reasons as Apple needs the filevault password to fix the machine.