I am in need of help with a persistant and unpredictable BSOD problem on my pc.

First...the SPEC:
CPU: AMD Athlon 64 3500+ Socket 939
M/BOARD: Asustek A8N SLI SE Socket 939 nForce 4 SLI PCI-E ATX
RAM: Corsair Memory CMX512 - 3200C2PT XMS3200 512MB CL2 (2 fitted = 1024Mb)
GRAPHICS: Connect 3D Radeon X800XL 256MB PCI-E DVI-I VIVO
AUDIO: Delta 4/10 PCI (on board sound disabled).
STORAGE: 1 IDE Hard Drive, 2 SATA Hard Drives.
DISPLAYS: HANNS-G (HC194D DVI monitor) Plus Acer AL 1914 (VGA)

History:
I built the pc two years ago and it has run endlessly for ages. I use it for audio recording, video editing amd some gaming - ALL OK.

However, in recent times I made changes but to be honest have rather lost the chronology of events that may have contributed to this recent problem.

Fact: Memory, CPU, M/Board, Graphics card and audio card have been in place all the time.
Fact: I added the display (DVI) in recent times
Fact: I updated the firmward in my DVD/R drive and didn't disconnect the hard-drives. I immediately had problems with one of the SATA's and had to reformat, repair the boot sector and reinstall windows.
Fact: I bought a new (USB) midi keyboard (CME) and installed drivers for it.
FACT: I got so fed up with the BSOD problem that I started again by reinstalling windows (XP SP2) and installed latest drivers for everything I could.
FACT: I ran memtest for nearly 24 hours - no problems (no BSOD either, strangely enough)

Overview of the problem:
I'm getting the BSOD very frequently these days....sometimes not at all in one session, another time 5 or 6 times in a couple of hours. It's hard to see what causes the problem. Sometimes it seems to be audio or video related - maybe playing a video file or recording audio. I often leave a large download running overnight and VERY rarely come back in the morning to see that the pc hasn't BSOD'd itself.

It's really ruining my enjoyment of my pc and my associated hobbies and would be EVER so grateful of one of you experts could have a look at my dump files and give me some advice.
I have already started using WINDBG and have explored the dump files, but despite my best Google inspired efforts I can't make head nor tale of them.
I've tried to help myself, but now I have realised my limitations. This is my first post and I am painfully aware that I am asking for help before being able to contribute to the forum in any way - I hope that you will look kindly on me....many thanks in advance!

It looks to be a hardware problem. As Memtest isn't perfect, try running just one stick of RAM at a time. Swap them over if it still crashes, or after a period of time where it hasn't crashed. If they both crash then try one at a time in another slot. One of the sticks of RAM or one of the memory slots may have died.

Peter, thanks for your reply.....

Out of curiosity, I wondered if your suggestion came from my general description or was it from the dump files? I would be interested to know what drove you that conclusion....I'm keen to learn here.

ANYWAY..... I pulled one stick of RAM and restarted. Machine wouldn't start - I just got beep error codes. In my enthusiasm to get on with things I didn't count the beeps but it looked like it was certainly struggling with that one particular stick. I immediately replaced the original stick and took out the 'offending' one. The PC started and has been running a 'mighty' 15 mins now.
Obviously I will need to watch this one for a while, so will let this run and report back in a while.

I'm feeling a bit excited that I (you) have got to the bottom of this - must make sure I don't count my chickens etc etc......

Thanks (so far) for your help - fingers crossed..........!!!

Follow up:

Out of courtesy to Peter (who helped me) and others (who might follow this thread for their own information), I'm providing a progress report.

Simple actually....all good, nothing bad. Two days of constant running, downloading, audio recording etc etc. Not one BSOD. I'm running on 512MB RAM of course, but there have been no problems at all.

The only thing left to decide is if the RAM was bad or (as Peter suggested) the slot itself. I'll run for a bit longer then move the 'good' RAM around the slots to eliminate the RAM or the board, finally.

I'll not bog the board down with constant updates, but I'm thinking that one or two follow ups will be of interest.

Thanks again.....!!

Paul