BadBoy7: Off the top of my head, try the detaching and reconnecting cable from your PC to the monitor, that is often the answer...maybe replace it if you have a spare, especially if it looks knackered

The same with the monitor, try a different one if possible.

If neither of those rectify the problem then it points to your PC itself..... take the side of your PC and try removing & putting the Video card back in.

After that, you are running out of possibility's, either the power supply or motherboard