I've had this kind of problem and it's generally one of three things.
One: The encoding is poor and the entire video needs to be re-encoded in order to fix it. Check the codecs, you might have encoded the video into a codec you cannot view properly on your hard drive.
Two: Drive speed, a slow drive can cause videos to do this and then crash the system with ease, unfortunately the only way to fix this problem is to get a faster drive.
Three: Hard drive space, if it's small it distorts videos and can sometimes cause them to stall and then crash, just clear more space or get a bigger hard drive if this is the problem.
Intellectual Property, Real Estate & Probate Attorney.