For starters (assuming you have Windows) right-click the icon for your disk,
select "Properties" (at the bottom), go to the Tools tab and hit the Check Now
button. Anything that weird could have either been caused by a disk error or
created a new disk problem.

Once you have cleared the disk as a suspect we should look at the software
on your system to see if there's anything which might be trying to fiddle with
your videos.