Computer hard locking pls help TIA

Hi I'm having some lock up problems and I have had it into 2 shops but it doesn't seem to lock when it's there. It locks at random times. I have taken every thing with it but the monitor. Here's what I have and have had done to it.

Newly installed on the system

AMD 3200 XP (400 MHz FSB) with older Volcano 9 heat sink and new OZ Thermal paste

Ultra 500W Power Supply

Maxtor 200GB SATA HD

And 2 case fans

I couldn't get my old copy of xp to install no matter what I tried. I tried the f6 install and I just wouldn't work. So I took it in to the first shop and got a new copy of xp with sp2 and they installed it and did all the updates. I take the computer home and notice my ATI control panel is not in the advance options tab and that the catalyst center won't launch. So I figure whatever and start surfing the web, then it just locks up. I start to parbreastion the drive and I get another lock up. So I run asus probe and so I can monitor voltage and cpu temps. Voltage seems fine but the +5 rating flops around a bit between 4.90 and 4.98. The Cpu temp is about 49-52'C and the mobo temp is about 28-30'C. Now have tons of air running in my case. So it not for the lack of fans

I took it into the 2nd shop and they had it for 3 days and couldn't make it lock up and they tested the hard drive and it was 100% fine they said. So I took in all my accessories and such to try to make it lock up there. Well I couldn't do it there. They suggested that the monitor was having trouble with my system and to check the year. So I did and it's April of 2000 manufacture date. I have never heard of a monitor doing this it possible? The shop owners our friends of mine and I'm sure not trying to sell me something. So I take the comp home run it for a day and it all goes well. The next day I'm using it and searching on the web it locks up again. So hear are a list of things that caused it to lock up.

3x in game called gunbound 2x when surfing the web and copyingdeleting files. When surfing 1x watching a video and copying files 4-5 X that I can't remember what I was doing.

The first shop also updated my bios form 1010 to 1013 could that have done it?

My system AMD 3200XP (Volcano 9 heatsink at max speed) Corsair PC3200 TwinX Memory 2x 512 ATI X800 XL (about 3 months old) Audigy Sound Card Maxtor 200GB SATA Hard Drive LG DVR Dive Light-on CDR drive

I'm out of ideas other than my Graphics card is flaky now for some reason is there anyway to monitor the chip temp on that card? Should I get a new heat sink for my CPU? Thanks Scott