Viviane,
Suddenly my one folder of selected raw files appear black when opened up in photo mechanic contact sheet. When clicked on they open individually but I want them to open up properly like they usually do. ONLY on this one folder, all the other folders open up normally. Help - I need to rely on all functioning normally again.
What version of Photo Mechanic are you running? What OS are you running? What kind of RAW files are you viewing?
If I had to guess, I would say that the cached thumbnails have somehow become corrupt. I suggest opening up the Photo Mechanic Preferences dialog, then click on the Caching tab, set the Cache to be emptied on Quit, OK the Preferences dialog, then Quit and restart Photo Mechanic. Then navigate to your folder again.
HTH,
-Kirk