Cheats for PS2 games

I'm having trouble getting my PS GameShark (V2?) to work, the disc loads on my old PS2 (v4 with a replacement laser), but not on my slim (90000). I used to use it, back when it was a current system, but a week or two back it gave me some error about the dongle and said it had to format it (???) or something and not to power off or take it out (so I didn't until it stopped), and now it locks up after booting but before selecting game or changing discs.

Any ideas? Or other ways to use codes...

Cheats for PS2 games