Hum,
The simplest solution is that it's a power issue...
(try a 500 power supply or convert a pc one)
Though it could be a software conflict...a program on the HD...Try running a minimum system...
And a worst case scenario, it's a virus or a dodgy memory module on the accelerator. (Virus scan, mem tester)
good luck.
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Half-dead cat found in box--RSCPA seeks Austrian scientist