Does your have the NVIDIA GeForce 7950 GX2 in it? First thing I would do is have only one monitor connected. If the fans are not kicking up correctly, that is a deeper problem. Open it up and see what, if any, fans are spinning when you are turning it on (especially on the video card). While you are in there go ahead and reset the BIOS. Make sure the power connectors are ok on the video card.
I hope the video card hasn't died, but I will go ahead and say it now, that with this combination of events, that as a definite possibility.
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