P4 system was unable to boot, and would randomly reboot. Got it to run long enough to generate a BSOD with MACHINE_CHECK_EXCEPTION. Disabled L2 cache in bios and boots fine, no crashes. I ran the microsoft memory diagnostic and it failed in the first pass (MATS+) at 004de000-1fff8000. No error, just froze up the program. Swapped out memory chip and ran again - failed at exactly the same spot. Disabled L2 cache in bios and ran again - no errors. Does this confirm the L2 cache on the processor has failed? I've never heard of this happening, but I suppose anything is possible.