Is it fully stable in orthos or prime95? Sounds like a stability issue my rig did same thing then figured out my board was dying or at lest hope it was board just got a BIOSTAR board and will start overclocking soon so we will see. Either it was board or my chip is going south in that case time to get a new one. More then likey the board it has overclocked 3 CPUs already all on air and all super high vcore and chipset volts.