|yeah sounds like there's just a crummy connection somewhere: check:|
1) Power to Monitor
2) Data (DVI) to Monitor
3) Data (DVI) to Video Card
you should also inspect your DVI connectors and make sure that none of the PINS are BENT. Make sure the cables are screwed in when you plug them in, to ensure a tight connection.
If you did not build this system, and another person or company built it, you should definitely bring this up to them. If there is a problem with the Video Card or motherboard and it never worked right, the manufacturer should be responsible.