Video troubleshooting

If your monitor in blank, make sure your computer is running by listening for fan noise and checking the LEDs on the front panel. If your PC won't boot check my earlier posts about startup problems here. Check your monitor power cable and video cable connected to the graphics card.
Press the power button on your monitor to see if it receives power. Then check brightness and contrast buttons to see maybe they are turned too low or too high. Try another monitor if you have a spare one. If the other monitor works, you know your problem.
Next check your Graphics Card. I will refer here to a standalone graphics card. To inspect it shut down your system and open your computer case. Make sure your video card is fully inserted in the slot. Take the card out and clean it with a soft brush (a makeup brush from your girlfriend if she doesn't mind). PCI express slots have a lever that you have to move in order to pull the card out, so be carefull. After you clean it, reinsert the card back to it's location, screw the bracket into place, reconnect video cable and restart the computer.
If this doesn't work use another video card to test your system. If windows starts with that spare card, you have to get it fixed or buy a new one.