This is hard to diagnose without getting hands-on. However, here's some things to try.

1.Check the power input.Make sure the cord is plugged in the wall correctly and in the power supply socket. Try a differant cord if possible.

2.Check the power connections inside the case. Make sure the motherboard and all other connections are tight.

3.Check the power supply output with a meter.

4.Check all the peripharels. Disconnect everything. If the power supply works by itself reconnect things one at a time until the problem occurs.

Hope this helps, if it doesn't, buy a universal problem solver-