I've just built an i7-950 system, with an ATI sapphire 4670, which runs off PCI-e power. It's occasionally crashing during gameplay: grey screen of death. No VPU recover either on windows 7, so it requires a complete restart.
I was using that card on an ancient pentium 4 before: it crashed a lot, until I underclocked it from 750mhz to 700. Then it worked fine. But that was on a crappy dell board, PCI-e 1.0. Now my new machine in running on a Coolermaster GX550 watt "80 plus" PSU, with a Gigabyte UD3R mobo. There should be no problem with power or the mobo.
I'm loath to even try underclocking: I should be able to overclock on this system.
Any ideas on what might be causing it? It's not something daft like my choice of particular PCI-e slot, is it?