I have been making a feature using FCP 5.1.1. Our editor and I have all the DVCPRO HD files exactly the same on each computer. when there is a new cut the fcp project is uploaded to idisk and I reconnect files. I discovered that we needed to nest sequences for my computer as it is slower than the editors. Today I uploaded the file. At first it would load. i reconnected all the media. One sequence was really long I started to get the spinning colour ball.After 20 mins I quit out. When I restarted FCP I got that horrible grey screen which tells you to restart .I have chucked out any caches I can think of. So I went back to old versions of the film. None of these earlier projects open. Projects totally unrelated open up fine.My data is on External lacie drives.So I disconnected these but no joy. Any help on this would be amazing.Many thanks

Boot in Single User Mode (hold down Cmd-S at boot)
At the prompt, type:

mount -uw /

Hit Return
At the prompt, type:

mv /Library/Preferences/com.apple.loginwindow.plist /var/root/.

Hit Return
At the prompt, type:

reboot

Hit Return
Your Mac should reboot and you should get back to the login window. You've lost nothing, as you only moved (mv) the preference file, should you need to go back to it for any reason.