Originally Posted by William
Personally I would want to use a working PS to test those units instead of a tester in this situation.
I would most likely guess motherboard, especially if those are cheaper HP/compaq or Acer/Emachines/Gateway units as the cheaper power supplies they use like to take board + processor and power supply when they fail because they fail into the on position which leaks excess current onto the board. Bestec power supplies used to be notorious for doing that.
That is why I wanted to know Randy what your PSU was especially since you indicated it knocked out both pc's. the problems I had been reading about were with Bestec power supplies.