Yes, it sounds like a PC issue.
Take the card and try it on another PC. Something's off and I understand that folk want the camera maker to fix what ever is amiss on the PC but they don't.
If you are having USB port issues a quick thing I try when I want to avoid charging the client for a full repair is to use the rear USB ports on the desktop. I can't tell what PC this is but try the other ports.
Also, I never have to use Quicktime as VLC PLAYER can play almost all those clips.