A 110V-220V Electronic Tester Screwdriver was inserted into USB Slot and the entire computer was powered off. I thought the PSU might have been short circuited. I pressed the power button several times and the computer did not turn on. I detached the power from the PSU and reattached it and then was able to turn on the computer again. Fully functional. -What might have happened and did that severely damage the computer?
Best guess would be you shorted the 5 volt power on the USB socket to the ground. The result is a dead short on the usb which may have caused the computer to shut down to protect itself. The usb controller should have tried to protect itself, but the socket may have been damaged (the gold trace may have overheated, burnt a little, scratched...)
Basic lesson - don't stick miscellaneous things into computer sockets. Why were you doing this with a 110/220 tester? There was nothing the tester could have told you.