Try Verbatim DataLife Plus DVD-Rs (Or at least some DVD-Rs that are of better quality than Sony and Memorex).
Use only DVD-Rs!!.
His PS2 may have a weakened laser (Or your PS2 simply has a better laser like a HD7).
But does he even see the FMCB logo at bootup?
EDIT: I've re-red your post, and you're hinting to me that he did.
I had a nasty problem when using Sony CD-Rs on my previous 2nd hand PS2 - a SCPH-39001. The PS2 was somehow unable to get a proper grip on the disc to spin it, and made some kind of scrapping noise (BSODs for every single game burned).
I had put a few layers of sticky tape around the disc's hub to give the PS2 better grip.
I don't know if this problem exists for SCPH-3500x PS2s, and/or for Sony DVD-Rs.
You should ask him to listen to the noises made by his PS2 after he selects "Launch CD/DVD", up to the point where it freezes.
We'll be looking for tell-tale signs of his PS2 struggling to read burned discs (Some kind of clicking noise).
Otherwise, it'll simply be some software problem.
--- About the loose wire inside his PS2 ---
It could cause his PS2 to malfunction, if it does cause a short-circuit.
He should get it removed ASAP (Although it may not be the cause of his PS2's problems here), if it's not well insulated.
SCPH-10000 S. MINOKAMO v1.01 (Defunct)
SCPH-10000 S. KISARAZU v1.00 (faulty)
SCPH-15000 S. KOHDA (With warranty seal!) :D
DESR-5100 S. EMCS