A computer is actually an assemblage of a number of different components. To understand the computer it is necessary to understand the role each component plays in the overall processing of information.
Problems can occur with any of the devices listed above.
A solution is apt to be found more quickly if we understand something of how each of these devices operates and how they interact. For your own safety, and the safety of your motherboard, always unplug the computer before open the case. Discharge any static electricity in your body and give the computer a chance to dissipate any stored charges as well. The outlet, power cord, power supply, or power feed to the motherboard may be at fault. Check the outlet, replace or reseat the power cord, open the case and examine the feed from the power supply to the motherboard, open the power supply and look for a fuse or reset, replace the power supply.