InDesign CS6 won't open files

InDesign CS6 won't open some files. No error message, simply returns to previous 'Open...' view. I've tried restarting, rebooting, resetting my InDesign preferences and re-unzipping the original zip file. I can still open previously worked on files, though. (Even in the second folder of unzipped files, it's the same files that I can and cannot open.) Any ideas? InDesign