You've got a Chokemax PSU. It can't handle the load, and is shutting off. Replace it with a quality PSU that has full range active PFC (no little voltage switch) and is 80+ certified. Antec, Corsair, Seasonic, PC Power & Cooling, and Enermax are among the better brands.
Under load, your 9800GTX+ uses only 10.5A. A 380W Antec Earthwatts or a 400W Corsair CX would power your system just fine.