Could be a couple of things, so try these steps:
1) Could be a faulty cord or power supply. If you're computer is under warrenty call your support desk and see if you can bring it to an authorized dealer/depot for diagnostic.
If this doesn't solve your problem then try:
2) right click anywhere on the desktop, select properties then select the Settings tab. Click the "Troubleshoot" button and follow the guide to see if you can correct the problem **Note** This is for Windows 2000, if you have another op system, the instructions may be slightly different.
3) Click Start, Control Panel and select the System icon. Select the hardware tab, then Device manager. If there is a problem with a device, you will notice either it having a Red X or a Yellow exclamation mark. Select any problem device, right click it, select properties and see it tells you there is a problem.
If you don't have a red or yellow mark. Find the listing for "Display Adaptors". Expand it, and select your Video Card (usually only one listed). Go to the Drivers section and make note of the Driver version and Manufacturer. Now follow this link to check to see if there is an updated driver.http://www.bleepingcomputer.com/tutorials/how-to-update-a-windows-hardware-driver/
Do the same for any device under "Monitor".
I'm no expert in computers, but I do consider myself an intermediate