Troubleshoot spontaneous shutdowns

I have a user who has a one year old PC. Periodically, the power just spontaneously shuts off. I checked the power connections, and all components, but still have the same problem. The user informed me that if he “whacks” it (AAAARRRRGGGGHHHHH!!!!!), it sometimes will power back up. Budget says, if it’s not broke don’t fix it, and if a part can be replaced, do that rather than replace the machine.

Out of ideas folks.