Picture freezing every couple of minutes

[clkio]

I have a ati 9600xt video card, and recently the picture in a movie or a game would freeze for 2 seconds every couple of minutes. Well, it doesnt really freeze, what happen is it moves very slow (like 2 fps) every couple of minutes then goes back to normal. I dunno why this is happening, I am using the lastest omega drivers. First I thought the video card can't handle games, but then I started playing a little flash game and it did the samething.