Did you by any chance apply some changes to the color profile of your monitor?
If so, revert to the original colorsync profile. FCP X is very picky about color profiles (I have no idea why).
Also, before doing such a drastic thing, did you try trashing the Preferences? Running FCP X from a different user account? Most likely there is some messed up setting that is causing this trouble, most likely a corrupt preference file, or layout. You could also trah the "Layouts" folder (it will be recreated when you start FCP X again). In the Finder hold down the option (a.k.a. "alt") key, and in the "Go" menu select "Library". In the Library folder navigate to Application Support/Final Cut Pro. Trash the "Layouts" folder.