If your power supply is connected to a surge protector, check that the reset was not tripped and turn the surge protector back on if it was. Check the power supply cord at each end - the wall and the PC; - make sure both ends are plugged in securely.
With both ends still connected to the wall and PC, follow one end to the middle of the power cord until you find the "brick" connection. Disconnect the cord at the brick. Wait 10 -20 seconds. Reconnect the brick.
See pictures below, for reference:
Your PC should now turn on.
If your PC does not turn on, please submit a ticket and let us know you already followed these instructions.