If you cannot see anything when the computer is booting, then the monitor may be on the wrong input (if it has more than one input - you should be able to select this from a button on the front of the monitor). Cable could also be faulty, as could the monitor, or the PC. Try your cable on a know good system, or a different monitor on your PC, or a different PC on your monitor to find out which component is faulty.
Touche
November 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.