[Magnus]

Try this... it's a bit geeky, but it might help.

To use fsck, you must run it from the command line. Unlike using your mouse to open an application to do something, you'll need to type a text command at the prompt (#) to tell fsck what to do. The Terminal application (/Applications/Utilities) and single-user mode are two examples of command-line interfaces in which you can type such commands. To use fsck:

1. Start up your computer in single-user mode to reach the command line.
   Note: If necessary, perform a forced restart as described in the Emergency Troubleshooting Handbook that came with your computer. On desktop computers, you can do this by pressing the reset/interrupt button (if there is one) or holding down the power button for several seconds. On portable computers, simultaneously press the Command-Control-power keys. If your portable computer doesn't restart with this method, you may need to reset the Power Manager.
2. At the command-line prompt, type /sbin/fsck -fy
3. Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:

   ** The volume (name_of_volume) appears to be OK

   If fsck found issues and has altered, repaired, or fixed anything, it will display this message:

   ***** FILE SYSTEM WAS MODIFIED *****

   Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
4. When fsck reports that your volume is OK, type reboot at the prompt and then press Return.

Your computer should start up normally and allow you to log in.

There's also this:

Disk Utility -> First Aid -> Repair Disk Permissions provides in red
Error: The underlying task reported failure on exit'

This was a nightmare for me to fix, but after I learned how it was easy. If you get this error and you have not already restarted your computer, open you sharing preferences and make sure you ahve not set the everyone group to 'no access'. If you have change it and retry to run the permissions repair. If you have already restarted you will need to startup using your install DVD and then open terminal. In terminal type the following to fix your permissions.

chmod 775 /Volumes/'Macintosh HD'
This will change your permissions and you should be able then to get past the grey screen.

Hope this helps someone.