I have a friend's MacBook that just gives the Gray Screen of Death on boot, combined with the fans running at "jet airliner taking off" speeds. I've tried everything to get it too boot: Safe Mode, ...

Uh-oh. You're in the middle of work when your laptop suddenly shuts off. No problem, you'll just press the power button and wait for it to reboot—your document is (thankfully) saved to the cloud, ...