There's the possibility that the creation of thumbnails from mov's is causing this issue - in that case I'd go into File Explorer, right click, View, and change the icons to something w/o a thumbnail...
BUT...
if you're on 8.1, I found similar threads that point to certain security updates:
http://windowsforum.com/threads/wind...9-help.200194/
Apparently if you uninstall those updates, and TURN OFF auto updates, it'll fix it.