Related to “Clips coming over as black in timeline”, FCP 7: just had this problem. Simple fix worked for me:
Go to ‘View” drop down menu. Under ‘Image — Image and wireframe — Wireframe’ options, make sure you don’t just have ‘Wireframe’ checked. Not sure how that happened, maybe some keystroke combination I’m unaware of. Anyway, checked ‘image’ and all was back to normal.
I knew it had to be something like this because these are the same clips I’ve been using for months, and they play uncorrupted in Quicktime.