yeah, Ultra PSU's are pretty poor quality. They are ok at first but after 12 months they are prone to leaking capacitors. Some people have issues with new ones also. http://www.overclockers.com/forums/showthread.php?t=634786
this thread show it has poor power output on its 12v rail, may be the issue. Also check the PSU fan is spinning and not overheating. If you can get your hands on a better PSU to test with that would be great. Not enough amps on 12v rail for that setup IMO. Its probably failing when it heats up after a few minutes then cant supply enough power.