a.) are all cables tight and secure
b.) is it plugged into a video card or plugged into the mobo? if vid card, test its connection into the mobo. Snug? If mobo, test the connection of the video receiver to the mobo itself, yes it can loosen sometimes.
c.) do you ever have problems booting, or booting into windows (your power management in the BIOS may be wrong)
d.) Have you tried different cables? cables crap out sometimes. look at the solder joints in the cables or the tiny little tines inside the cable's connector. is it missing any tines? is there any loose soldering?
e.) have you tried plugging the power cord into a different outlet (yes this is stupid but sometimes power outlets in older houses can "fizzle" out
f.) is it possible to test your connections with a diff monitor or TV or something. because your video card may be dying. or is this the one plugged into your 360?
If all the above fails, SORRY COMPADRE!!!!!!