Interrupt Clash
Using the System Tabs applett in Control panel - Check to see if there's a memory or interrupt clash problem - I know modern PC's can share interrupts (like this one ) but you may just have a clash.
Control Panel, System , Hardware , Device manager , View , Resources by connection. then select DMA or Interrupt request.
Sorry, I missed the obvious - Faulty RAM - Run Memtest86 or similar as a fault finder.
CAT III
(Pentium 4D, XP3 , 3GB Ram , NVidea Go6800 behave alike, 80 Gb x2 Non raided, DVD broken by CAT III - Re Dog bite , Dog not fed - Dog Irate - Dog displayed Teeth and used them)