Have you tried trashing your preferences?
Faults like this can often be fixed by clearing out FCP X's preferences (for some reason, they get knotted up from time to time).
Download Digital Rebellion's Preference Manager (free, simple to use, and quite safe).
With Pref Manager, you can backup the Prefs first, then if trashing makes no difference, you can restore all your settings.
If you trash them and don't restore them, you will need to go over all your FCP X settings again, so it's a great idea to backup Preferences from time to time when FCP X is working well, then you can ditch the bad prefs and restore from your (Digital Rebellion) backup.
Can't guarantee it, but it's worth a try.
We just started having the same issue, and haven't been able to figure out a solution just yet. I submitted a bug report to Apple. Interestingly, the program seems to somewhat usable. It will play video. But that splash screen with "Loading Compressor Support" will just not go away. I don't have the new Compressor installed, but I do have a much older version on the computer. I hope we can soon get this issue resolved.
Ok, got our Final Cut Pro X back on track, and here's what we did. I simply deleted the com.apple.FinalCut.plist file from the Library folder and that did the trick. Honestly, I wasn't too keen on downloading third party software from an unknown source as suggested above, so I'm glad I got it to work without having to do so.
The Library folder in Lion is hidden by default, but you can get to it easily in the Finder by selecting Go > Go to Folder and entering ~/Library/. This will take you directly to the hidden folder and then you can navigate to the Preferences folder to find the preference file.
What a relief. Hope that maybe helps you as well.
Digital Rebellion's Preference Manager is a highly respected application. If you search for it on this or any Apple Professional Application discussion site, you will find many references to it.
It is utterly reliable and saves an awful lot of time.
Trashing preferences seems to be a regular requirement - especially with the buggy FCP X. Your method of trashing your preferences was incomplete, and requires manual resetting of each individual preference every time you do it.
With Preference Manager, you can trash the corrupted preferences in FCP X and all the other Apple Pro Applications if you wish, and re-set them with a single click of your mouse.
I would also recommend Pro Maintenance tool from DR, there are lot of option to deal with your system and specially the option: House Cleaner which removes lot of FCP X files not needed. But it is not cheap. http://www.digitalrebellion.com/promaintenance/