please help - inspiron 5150 video slow down

If I play any video it will work right for a little bit then the video will slow down for ten seconds then go back to normal. I cannot watch any video or capture videos from my camcorder because of this. how do I fix it? what is wrong.

I have no back ground programs running and I think I have the drivers and I reinstalled xp like a week ago, I have the same set up on other computers with no problems. how do I fix it. also the dell call support is useless they threw me from person to person and repeatedly put me on hold without helping me at all.

please if anyone knows how to fix this tell me.