Hard drive would mean he can see the boid screen, which you don't suggest is true. Sounds like a loose/ dodgy card somewhere.

I had the same seemingly random problem with my soundcard. Once I took it out, all problems went away. He should try taking things out a board at a time and see if that helps.

The other issue could be dodge power upply or too much power draw, stopping the machine from getting to the BIOS screen even. This normally only shows when you turn on, and goes away on a soft reset.