Re: Boot problem with GTX 460
the on board graphics might still be enabled in the bios, and when you boot into widows it takes an additional full power cycle to re-enable everything. then the nvidia driver realizes what's happened and re-asserts itself, requiring an additional reboot before it wakes up. rinse and repeat...
it might be something like that. try to narrow down the problem (is it a hardware issue, is it the amd drivers, is it the nvidia drivers, is the pc suffering from lycanthropy, etc.)