AGP glitches / crashes - sound bites

This is a bit long but wanted to provide all the details I could.

the system:
MOBO - ECS K7S5A
CPU - XP 1700+
RAM - 512 DDR
VIDEO - NVidia Ti4200 AGP 128 MB
OS - W2K / XP (dual boot)

the symptom(s):
1. After booting and the desktop displays the monitor flashes 4 times off and on.

2. When doing video capture, video editing or graphics composition computer powers off and reboots.

3. The sound is muted. At full volume it is very quiet.

the events:
1. this all started when the original OS was removed and replaced with the dual boot setup. The problems are identical in w2k and winXP.

2. Looking at device manager, there are about 10 devices which are sharing an IRQ with the video card.

3. According to MS there is no way to manually assign an IRQ in w2K or XP without reinstalling the entire OS with a 3rd party HAL.tech article

I have checked the following:
1. Tried the video card in another machine.

2. Unplugged all extra devices (to see if power supply was strained)

3. updated drivers for devices such as sound and vga

4. removed and reinstalled video / memory

According to MS IRQ 9 is supposed to contain 'pci for irq steering' but i do not see that in device manager.

I just don't what else to do. Has anyone had similar problems?
Thanks in advance for your help.