Q: Finder crashed and now I can't access to anything !

Try these in order testing your system after each to see if it's back to normal:

1. a. Resetting your Mac's PRAM and NVRAM

    b. Intel-based Macs: Resetting the System Management Controller (SMC)

2. Restart the computer in Safe Mode, then restart again, normally. If this doesn't help, then:

     Boot to the Recovery HD: Restart the computer and after the chime press and hold down the

     COMMAND and R keys until the Utilities menu screen appears. Alternatively, restart the

     computer and after the chime press and hold down the OPTION key until the boot manager

     screen appears. Select the Recovery HD and click on the downward pointing arrow button.

3. Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the Utilities menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility. 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 main menu. Select Restart from the Apple menu.

4. Reinstall Yosemite: Reboot from the Recovery HD. Select Reinstall OS X from the Utilities menu, and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

Do this:

Install or Reinstall Yosemite, Mavericks, Mountain Lion, or Lion from Scratch

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

How to Clean Install OS X Yosemite

OS X Mavericks- Erase and reinstall OS X

OS X Mountain Lion- Erase and reinstall OS X

OS X Lion- Erase and reinstall Mac OS X

Note: You will need an active Internet connection. I suggest using Ethernet if possible

            because it is three times faster than wireless.

When you are in the Recovery HD's Utilities Menu and open Disk Utility, try to clone your drive to an external, blank, formatted backup drive.

You can try Target Disk Mode as well.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Console in the icon grid.

Step 1

For this step, the title of the Console window should be All Messages. If it isn't, select

          SYSTEM LOG QUERIES ▹ All Messages

from the log list on the left. If you don't see that list, select

          View ▹ Show Log List

from the menu bar at the top of the screen.

In the top right corner of the Console window, there's a search box labeled Filter. Initially the words "String Matching" are shown in that box. Enter the name of the crashed application or process. For example, if Safari crashed, you would enter "Safari" (without the quotes.)

Each message in the log begins with the date and time when it was entered. Select the messages from the time of the last crash, if any. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.

☞ The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

☞ Some private information, such as your name, may appear in the log. Anonymize before posting.

Step 2

In the Console window, select

          DIAGNOSTIC AND USAGE INFORMATION ▹ User Diagnostic Reports

(not Diagnostic and Usage Messages) from the log list on the left. There is a disclosure triangle to the left of the list item. If the triangle is pointing to the right, click it so that it points down. You'll see a list of crash reports. The name of each report starts with the name of the process, and ends with ".crash". Select the most recent report related to the process in question. The contents of the report will appear on the right. Use copy and paste to post the entire contents—the text, not a screenshot.

I know the report is long, maybe several hundred lines. Please post all of it anyway.

If you don't see any reports listed, but you know there was a crash, you may have chosen Diagnostic and Usage Messages from the log list. Choose DIAGNOSTIC AND USAGE INFORMATION instead.

In the interest of privacy, I suggest that, before posting, you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header of the report, if it’s present (it may not be.)

Please don’t post other kinds of diagnostic report—they're very long and rarely helpful.