.mpg video and audio playing too fast on wmp9 and ATI file player

My .mpg video files are playing way too fast on windows
media player AND ATI file player. They've played fine in
the past. I tried the files on 2 other pc's and they play
fine, so the problem is not in the video file. here is my
system configuration on the problem pc:
Windows XP Pro w/SP1-updated
Abit AT7/MAX2 motherboard
768MB PC2100 DDR ram
ATI 8500DV 64MB video card-updated drivers
AMD XP2400 CPU
2-80GB WD 7200rpm hard drives in a RAID 0 striped array

I was using the built in sound(AC97 avance) on the motherboard.
I installed my Soundblaster Live! X-gamer 5.1 sound card
and disabled on board audio in my BIOS to see if that fixed
the trouble, but the problem remains.
I checked the device manager and all devices report to be
ok and working properly.
The video and sound are in sync.
I then restored my system using a ghost image from 3 months
ago and the problem remained. Then I updated windows but
still the problem remains.
Any help would be appreciated,
JerryJ