A non techy mate's pc 'stopped' working after a power surge at his home, he asked me to have a look as it would not boot without hanging and could not enter BIOS. He brought it round to my place and plugged it into my kvm switch, it booted enough for me to initiate a scandisk which revealed: "first allocation unit is not valid" errors. Scandisk fixed these. I then run the machine, rebooted etc on and off for 24 hours with no problems. I checked it with his mouse and keyboard, and other than an apparent fault with the ‘del’ key not working (hence could not get into BIOS) it seemed fine. Apparently fixed I gave it back. When he got it home he said ‘it was the same as before’ still had errors and he had had to turn it off at the plug. He brought it round to mine where, once again I connected it to a kvm switch, turned it on, allowed it to go through its disk check (its FAT32 so it would scan after a switch off at the mains) where it found one "first allocation unit is not valid" error and then worked fine. He took it back only to bring it straight back saying that he was getting a message ‘no support’ and a press F1 keyboard error. I tried it with a different keyboard but get the same error message. Seemingly the keyboard controller on the motherboard has decided to give up the ghost.
That still leaves me wondering where exactly the fault is and whether I should recommend a whole new pc, new motherboard, motherboard and PSU or what?