Computer Shutting Off

[Icemastr]

My computer ran fine with the 2400XP processor except it was having problems with locking up every once in awhile, freezing while playing games, etc. I thought it might be dust was causing the CPU to overheat so I airsprayed everything out, my CPU fan was really dirt, it made a decent difference in CPU temps but still had the same problems so I got this case that is new with a 550W power supply from my friend and still had the same problems. I wanted to upgrade my processor and ram anyways so I got a 3000XP cpu and an additional 512 mb of kingston PC2700 ram. Now in addition to locking up while playing games the CPU will not run any faster than 1167mhz. Anytime I try and run it at the default rate of 2167 mhz the computer will get into windows, run for a minute then shut down. I have to unplug it and restart it then the computer shuts down before it even loads windows, do the same and it shuts down right after getting past the bios, do it again and it shuts off right away. I tryed backing it down to 1700mhz and the same thing. I could get it to run at 1167mhz but still would lock up everyonce in awhile. So I ended up getting a new Asus A7V800 motherboard. Same problems but now I am at 1300mhz, any faster same thing.

Old Specs
Athlon 2400XP
512MB PC 2700 Kingston DDR Ram
Asus A7V8X-X Via KT400 chipset motherboard
400w power supply
Radeon 9700 Pro agp card
Soundblaster Audigy 2 sound card

new things added or changed
Athlon 3000XP with new CPU fan
1024MB PC 2700 Kingston DDR Ram (2 Dimms)
Asus A7V800 Motherboard
550W Arrow power supply
2 Case fans

All I can think of is the power supply sucks, or the ram is the wrong speed but neither makes sense to me. I have no other ideas. Anyone know what it could be? I know it isn't getting to hot because it is shutting off at like 49celsius.

 

[MaMMa]

try memtest or prime95?