Also another thought, do you have on the m/board cd, a programme for looking at the temp of the cpu while it's running. With a previous machine, 2 years ago, I had many hours of frustration with a simular lockup, rebooting system, only to find the power supply fan was insufficient to cool the machine, (the top of the case was almost untouchable), only recirculating the warm air, case fan installed, functioned satis.