Horrible video overlay!

Hmm...I have no idea what is causing this, but it's really starting to irritate me! I have a backup computer I built out of spare parts I had. It's pretty decent...Duron 850, 128M RAM, GF2 GTS(AGP), Voodoo3 3000(PCI), on-board via sound, 3.2G HD, 40x CD, and some video capture stuff.

Here's my problem...when I go to play just about any type of video file, the overlay is full of vertical green lines. Also, the sound is sometimes effected, and has a constant buzz in the backgroud... I think I did try one MPEG1 video that acctually didn't cause any problems. But everything else is horrible. I've tried to update to DirectX 8.1, update some codecs, and update Media Player, but it's all the same...

Any ideas?