Quicktime alternative typically has a reverse-engineered version of QT that is several versions old. I don't know if it's even being updated any more. I wouldn't trust it. Media Player Classic can also be problematic, and the last time I used it, it couldn't do anything VLC couldn't do and some things not as well as VLC. Try using VLC for most files, and Windows Media Player for AVI files that VLC won't play (such as Lagarith and UT AVI files). If VLC plays your MOV files from your F: drive properly, then the files are OK (ditto for WMP). If not, then CJRodgers87 is likely correct about corrupted files.
Do the files import correctly directly from the memory card? It's not a good idea to edit directly from the card, but it may be illuminating to see if the files import OK from there.
Jeff
