Random BSOD even after reformat

Im working on my friends computer and it keeps crashing.

Specs:
MSI MS-7104 Ver 3.0
Intel Celeron 2.2 Ghz
1024MB Kingston PC2700 (New)
nVidia GeForce 6200 256Mb AGP 8x
260GB Hitachi Hard Drive
Sony DVD/CD Burner
450 watt Thermaltake PSU

At first the on-board VGA stopped working. I replaced it with a AGP card and it worked fine for a month, before it started having problems.
The original 1 of the 2 original ram sticks, in bank 1 stopped working. Kept getting random BSOD's, so I tossed the old ram and left in the new Kingston stick.

Installed the new stick and it still BSOD's randomly. They were very random but I got one written down.

0x0000008E (0xC0000005, 0x00000000, 0xB9255538,0x00000000)
IRQL_NOT_LESS_OR_EQUAL

I thought Ram? So I ran the stick on both DIMM slots with memtest86 multiple times, and it found NO errors.

CPU temp? 40oC at idle...cleaned heatsink, applied AS5......still BSOD

Next, I broke the system down to the basics... PSU, CPU, RAM, Video card, HD, CD drive. STILL BSOD.

Next I swapped out the PSU... still BSOD
Test hard drive with HDAT, Hitachi drive fitness....passed
Reformat HD and reinstall Xp Pro, not loading any Mobo drivers... still BSOD
Installed Mobo drivers, minus nVidia drivers... still BSOD
Removed front panel USB connectors
Swapped HD, full format, reinstall OS.... still BSOD
Swapped Video card..... still BSOD
BIOS is up to date, only add-in card is the Video card.

I am at a loss, spending wayy too much time on this thing. Any help would be appreciated.
I know mini-dump files would be some help, but I just re-formatted the HD again and havent reloaded the OS yet and im beat for now.

The only things I havent crossed out are the CPU and Mobo. Are there any DOS based programs that I can use to test it?
The only boot disk I have ATM is Hirens. Im guessing the Mobo may have crapped out, especially since the on-board Video broke. The on-board LAN works intermittently.
The system was built by another dude two years ago. I dont see any damge on the Mobo.

Please help! Thanks in advance!!

Sounds like the Chipset is knackered to be honest, it seems to be having problems across the entire spectrum, so I'd say it's the motherboard.

Thanks for the reply.

My first mini dump files were pointing to AVG 8.5. So I reformated and swapped out the IDE cables.
System was stable until I installed the latest chipset drivers from MSI.
Once chipset drivers installed It would also fail to install PCI to PCI bridge in "add new hardware".
I restarted the PC and instant BSOD. So I reformatted and got the chipset drivers directly from VIA. Still BSOD.
Minidumps 3 out of 4 pointed to ntoskrnl.exe as the problem. Fourth one pointed to wdmaud.sys as the problem.

So yeah.. Im still at a loss. I think the mobo is screwed. I just have no way to test the CPU and Mobo at the moment.

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I have just done a visual inspection of the motherboard. Everything looks fine, no popped caps.
The only thing that looks out of the ordinary is that the motherboard is flexing upwards on the top (cpu side) but its perfectly flat on the bottom (pci slot side).

Im wondering if this would cause problems? I know that on Xbox 360 mobos it will cause all kinds of problems.

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Well I dont think the flex is the problem. I just removed the Northbridge heatsink and to my suprise 1/2 of the crappy thermal paste that was there is gone!!
It melted right off, replacing it with AS5 ATM. I hope it works or im done with this thing.

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So it still BSOD even after adding AS5 to the north bridge and a reformat.

I got a theory... The north bridge must have overheated from not having thermal grease on it.
It caused the on-board to stop working properly. It also damged the northbridge permanently, causing it to work properly intermittently.

Is that a possibility?