Locked or dead video, repeating sound.

Description:
Within games, move file or dvd playing, I am getting periodic lockups of my PC. The video locks in frame and the sound that was being played repeats over and over at an extremely fast rate. Another variation is that the screen goes black (the monitor is still on and active, but the video is black) and my speakers crackle. Either way I have to reboot to bring the system back.

I've been having this problem off and on for the last year, now its gotten to the point that I can't do anything intense on the computer for more than 10 minutes before it locks.

In the last couple months I have replaced:
Motherboard, power supply, CPU, HeatSink, Video Card and sound card.

At first I thought it was a sound issue, but after using 3 different sound cards with the same result, I'm satisfied that it isn't.
Then I thought it could be that my CPU is over heating as it had been at 50+Celsius after rebooting, but I've replaced my heatsink with a Volcano 7+ with CPU temps now under 40C, its still locking up. Could this be a memory issue? Its the only thing I haven't swapped out yet to be honest. I haven't swapped out any HD's or other drives, but I doubt they could cause this type of error.

Below are the specs for my PC along with a list of other pieces of hardware that I've had this same problem with.

ECS K7S5A v3.0 (SiS 735 Chipset)
AMD Athlon XP 2000 w/ Volcano 7+ Heatsink
512MB PC133 Micron SDRam
128MB ATI Radeon 9500 Pro
60GB Maxtor ATA100 HD (7200 RPM)
Turtle Beach Santa Cruz Sound Card
3com Etherlink NIC
Acer 431W AMD/Intel Approved PSU
16x40x Pioneer DVD-Rom
8x4x24x Yamaha CD-RW

Replaced:
ASUS A7V133 Motherboard
AMD Athlon 1.33GHz TBird
64MB DDR Hercules GeForce2 GTS Pro
Philips Acoustic Edge Sound Card
Enermax 400W PSU

Any help any of you could provide would be greatly appreciated.

Also, I keep my PC updated with Windows Updates, video driver releases, etc, so this isn't a case of needing updated drivers/bios.