My PSU gave up the ghost about 3 days ago..... (it was a cheap on 550w). This ran the PC fine for about a month.... I have replaced it with my missus's brothers spare one. 700w with 16A on each 4 12v rails. Now new issues. PC is fine apart from when the GPU is under load. If I underclock the card by a 1/4 then it is stable again. Stock clocks the PC turns off and restarts within 1min of loading BF3. When i underclocked it it played for 1hr without issues. I know everyone is going to say its the PSU but it ran fine for 1 month on a 550w s**t PSU! Spec is i5 2500k @ 4ghz, GTX 570, 16gb Corsair Dominator, 120 gb SSD.
And what was the make/model of the 550W? A system with a single GTX 570 requires a 550W with two 75W 6-pin PCIe power connectors and at least 40A on the 12V rails. Amperage on the 12V rails is more important than the total wattage rating of the PSU; modern PCs draw most of their power from the 12V rails and the CPU/GPU are the largest power draws. Have you tried taking the CPU to stock clocks and varying the GPU clocks?