Videos are suddenly "choppy"

I have a question. I have a number of videos I've downloaded from this site and they were working great, but for some reason, all of a sudden they have started playing in kind of a choppy way. In other words, they will play for a few seconds, and then pause, and then start playing again. They do this over and over throughout the video.

Does anyone have any idea what I can do to fix this, or are my videos all toast? I'm hoping I can fix it, because I love these old vids. There's nothing like the classic stuff!

Any help would be greatly appreciated. Thanks!