The cord could be at fault. Try borrowing a cord from someone you know to see if it corrects the issue. If that does not work the problem may be the ps2's AV port. Try wiggling the cord around to see if you can get some sound to come out of it. Although unlikely, if you have only tested it with one game the disk could be scratched enough to cut out all audio tracks.
Good luck with the repair :)
Bosnoff
August 2007