1. Make sure monitor is powered on and the cable is plugged into the back of the computer tightly.
2. When you turn it on listen for beeps. If you have any, then you have a hardware problem.
3. If one of the lights flicker after powering on, and all of the above are negative, you probably have a problem with either the monitor or the video card.
(Note on a LCD screen: if the light on the monitor is yellow - instead of green then your resolution/clock rate may be too high.)
Mr K
November 2008