|So then you DON'T see a blue screen? That is an indication that Windows is trying to start. |
If you got that far at least once then I would guess it isn't the CPU. I would strip it down to the bare hardware needed to boot and try again. No drives, 1 stick of RAM, keyboard, graphics, monitor. Disconnect all case to board wiring. Remove all external hardware.
If you have another graphics card you could try that.
Probably the power supply. Just because you see signs of life doesn't mean the PSU is actually OK.