1st - Reinstall your drivers
2nd - Check all the cables are connected properly. You'd be surprised by the amount of problems caused by loose cables. Try using a different cable, too.
3rd - Try moving the graphics card to another port.
If all these fail, and the monitor works without the black outs, you need to get a new graphics card. If the monitor black outs on another computer, and the cable is fine and everything, then you need to get a new monitor.