Stuck on blue screen during boot up

Try this:

Clearing Caches to Fix Login Problem

You will need to type some Unix commands. If you are not comfortable with this, I don't know of anything other than a re-install. But if you are careful, you should be OK. I recommend you print this out in a largish mono-spaced font so you don't miss any spaces (or add extra ones). Note that case is important.

Be careful. Some of these commands are dangerous, since you are going to be root.

Start up in Single-user Mode. When this has finished you will see a prompt ending in '#', although there may be other messages. Enter the following commands after the prompt:

/sbin/fsck -fy

Press RETURN. Wait a few seconds for 8-10 lines of output. If the last line says repairs were carried out, repeat this command until you get a message 'The volume <yourdiskname> appears to be OK'. Then continue with:

/sbin/mount -uw /

cd /Library/Preferences

rm com.apple.loginwindow.plist

rm com.apple.windowserver.plist

cd /Library/Caches

rm -r *

cd /System/Library

cd /System/Library/Caches

rm -r *

reboot

Press RETURN after each command.

This should now take you to a proper login screen after the normal boot sequence. You should then Repair Permissions by using Disk Utility (in your /Applications/Utilities folder).

How long have you waited at the blue screen? Sometimes it may take a while to get over, but after that it will continue normally.

Try booting in Verbose mode (hold Command-V at startup) to see if the system pauses when loading any specific item during boot. Additionally, do you have any peripheral devices attached to the system (printers, scanners, hard drives, etc.)? If so then remove them and see if that helps anything.

Finally, try booting off your OS X installation DVD and running a permissions fix on the boot drive using Disk Utility (available in the Utilities menu after you select your language). Running permissions fixes is recommended to do from the boot drive itself, but since you cannot get the system to boot this is the only alternative. If you then are able to boot the system, re-run the permissions fix routine from the boot drive.

If you have tried all that Apple recommended then the next step is to reinstall OS X, but you need the installer discs to do that.

Reinstall OS X without erasing the drive

Do the following:

1. Repair the Hard Drive and Permissions

Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

2. Reinstall Snow Leopard

If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.

Download and install the Combo Updater for the version you prefer from support.apple.com/downloads/.

Yes. I would recommend getting a SL installation DVD for your system.

Glad to help, but sorry no fix for you.

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