A friend of mine's computer locked up one day. She reached around the back as she thought there was some sort of reset button there. She found a switch of sorts and flicked it to its other position. PC was far from happy having had its power supply switched from expecting 240 volts (UK standard) to expecting 110 volts (though still receiving the aforementioned 240). A large bang was the result. Fried the motherboard completely.
She did have a bit of a track record - it was the 3rd PC she'd lost within 12 months! I did manage to recover data from the HDD, though that was rather flakey about powering up at first.