I had a very peculiar thing happen in FCP 5.1.4 yesterday, and I was getting ready to post a frantic question until I stumbled on the solution. This is bound to happen to someone else (probably already has) so I'll offer my workflow.
I had been using FCP but had switched to other applications, while FCP was still open. When I switched back to FCP I got an utterly black screen. The dock was in "hide" mode (but I never set it that way) so I could go to other apps, but always a fully black Dell 24 inch screen when FCP came to the front. I quit FCP and opened it again - still black. I restarted the computer, opened FCP with no project - still black. Dropped a project file on FCP to open it - still black.
If I moused to the top of the screen, the FCP menu bar would appear, and I could select things to my heart's content, but nothing helped. I tried ctrl-U for a standard layout, tried other layouts, no better. Here's where it really got weird: As long as FCP was not the frontmost window, I could see the entire interface behind what was in front, just like it should be, but if I clicked on it to being it to the front everything went black again. I figured trashing preferences might solve this, but I didn't want to do that yet because I had it the way I liked it.
By this time you may have figured out what was going on, and last night I was literally lying in bed thinking about it and suddenly realized what it might be. And this morning I confirmed what it was. I brought up the black screen and pressed Escape, and there was FCP back again! I had been in Digital Cinema Desktop Preview, at a black section of a timeline, when I switched to another app, and there I was until I was able to exit DCDP the "normal" way.
I find it utterly amazing that this state survived FCP being restarted repeatedly, and even survived rebooting the whole computer. I wonder if trashing preferences would have fixed it? What I realized is that never before had I switched out of FCP while DCDP was active, I always escape out of it when I'm through watching.
Thanks for listening, Doc, I feel better already.
Scott