WARNING: Before you start troubleshooting remember that you are dealing with electricity that can KILL. http://www.kitchentablecomputers.com/static.php - rules
Only work inside the computer case when the power has been switched off and disconnected. Never open the power source. Some of the below steps recommend removing physical parts within the computer. While in the computer it is highly recommend that you be aware of ESD and its potential hazards Causes a Computer Monitor to Go Blank
b> While a blank screen may be caused by a general power outage, more often it's a problem with the screen itself. It could be a loose video or power cable going to the monitor. If that's the case, you can get the screen working again and be back in business in a few minutes. b> Power Problems
All the power might be off due to a bad outlet, switch, fuse, or circuit breaker. If you hear no sound coming from the computer and its power light is off, check the power connection and breaker or fuse. Video Cable
Many times the cause of monitor blackouts is a loose video cable connection. This might happen if you move the monitor or the cable. The video cable runs from the back of the computer to the monitor. It has a multi-pin connector on each end and both of them screw down securely. If the screws aren't tight, either connector could become loose. If that happens, the video signal could stop suddenly and make the picture go blank. Check both ends of the connector to make sure they're firmly seated and the screws are tight. The cable itself might be bad.This is unlikely, but possible. b> Display Power
The monitor must have power. If the power light isn't lit on the monitor, it may have been turned off or become unplugged. Press the power button to make sure it wasn't accidentally turned off. Make sure the monitor is plugged in. If it's connected to a power strip, check that the power strip is on. If that checks out, unplug the monitor and try a different outlet. Power strip sockets can sometimes fail. Flat-screen monitors may have a power-brick-style adapter. It, too, has connectors. Follow the power cable from the monitor's power plug back to the monitor. About halfway up you'll find a thick rectangular plastic brick. The power goes into a modular-style equipment socket. This can become loose. Follow the wire the rest of the way to the monitor. It connects to the back of the screen with a small round plug. Check that it's firmly plugged in. If everything's plugged in right and the power light on the monitor's still off, the power brick might be bad. b> Video Card
Some computers have a separate video card inside. It may come loose and cause a blank screen. If this is the case, open the computer and inspect the video card. Sometimes removing and reseating the card will fix the problem. If it has to be replaced, most video cards are not expensive.