...fry a motherboard/CPU from lack of power? My friend plugged in a 20 pin in a 24 pin and powered it up. He said it made a high-pitched noise and he unplugged immediately. Could this have fried his parts?
I wouldn't have thought so. You can damage hardware from spikes etc, but I that wouldn't have damaged it.
If it made a high pitched squeal, it was probably because he didn't have the video cards PCI-E power connectors plugged in.