Random 2500+ Crash (PLZ HELP!)

I just upgraded my Athlon T-Bird 1Ghz to an XP 2500+ with the Barton core. I popped it in and booted up and was surprised to find that it wouldn't even post. After a couple minutes I realized that I hadn't updated my BIOS to accept it. I'm running a Leadtek K7NCR18D with an nForce2 chipset and it has never given me problems before. After updating the BIOS in Dos and Windows, I got the computer to recognize it as a 2500+ but about 10 minutes into some benchmarking with 3dMark it just randomly crashed. No blue screen or anything, just a flat out cut of power.
I wouldn't have thought anything of it but as soon as I got back into windows it did it again in about 30 seconds of use. I'm not overclocking the processor, the temperatures of the motherboard and CPU are stable (42C for mobo, 50C for CPU) and the ram isn't running any faster than it should be. These random crashes have never happened before with my T-Bird so I don't suspect it can be anything but the CPU. My only idea is that maybe the Vcore isn't stable. It's running at what it told me was default (1.6V). What's going on?

System Specs:
Athlon 2500+ Barton Core
256mb PNY PC2700
IBM Deskstar 40GB
Leadtek K7NRC18D
ATI Radeon 8500LE
Windows XP Pro

ya shitty power or boared don't exept barton
maybe it's your cooling barton's are recomended to have copper based heatsinks
not sure tho

As far as I can tell my power supply hasn't had any problems. It's a 350W Codegen PSU, about 6 months old. My heatsink definitely isn't the problem. I'm running a thermaltake volcano7+ at the medium setting, about 5000 RPM. I really don't know what it could be. Anyone have any other suggestions?

I put my old CPU back in for a couple hours and there was no trouble. Today, I clocked the ram down from 166 to 160 just to see if it was more stable, to my surprise it hasn't crashed in about 3 hours of strenuous gaming. I guess that's a temporary solution, but a definite answer would be more welcome.