I've got a HD clip that is offline in the timeline, but I can see the footage in the FCP window.

The original quicktime is nothing but a white screen, but it runs for 11 minutes, which is the original time of the clip.

What is going on?

The footage is there, I tried exporting the footage that I can see in my FCP window, but when I open it, it's offline as well.

I really need this clip, what do I do?

I'll explain more if this makes no sense, I'm not really understanding it myself.

Your thumbnail cache for these files, for whatevr reason, is not correctly updated ... the easiest solution is simply to delete you thumbnail cache folder. FCP will then regenerate new thumbnails. You can see the location of your thumnail cache folder in the Final Cut Pro menu > System Settings window.