My best bet would be one of two things. You don't have enough voltage (for the cpu, or the mem, or both), or your SDRAM memory is crapping out...heat could be an issue, too. Have you tried burning in the system, and if so, for how long? Are the components new? What is the rest of your system specs (HDD, any PCI cards, AGP card)? What is your voltage set at for the cpu and mem? What are your temps?