First check the computer's power cord to make sure it is completely plugged into the wall socket. If you are using a power strip, make sure it is completely plugged into the wall socket and that the power switch on the power strip is turned on. Some power strips also have a built in circuit breaker which usually looks like a black or red button near the power switch. Press the button to reset it and see if that solves the problem.
For requests that do not fit into any specific category but still require technical attention