Check the connections, make sure his video cable hasn't come loose.
Listen very closely to the disc after a minute or so. Does it just spin constant, or does it sound like it's loading? If it sounds like it's operating normally, get a new A/V cable. Or, if he's using the optical audio cable, is he getting any sound from it? (i.e. try to determine if the A/V cable has crapped out before replacing the entire system).
If that's not it, turn it off, unplug it for 1-2 minutes, then try again. That's about as "hard" a reset as you can get on something like that. If it were a computer, and still messing up, I'd suggest resetting the BIOS at this point, but you can't do that on a game console.
If none of that works, get a new PS2, or just take a break until PS3 comes out.
