With the PSone games, try connecting the PS2 directly to the TV to see that everything works there. Then try running it through the receiver from several different inputs (DVD, DTV, etc.), just to make sure one of them isn't messing it up. Other then that, I don't know what else to check. There's an options menu that you can open up when you start the PS2 without a game in, check in there for anything that might be causeing this.
Also, try using a couple different PSone games, just to make sure it isn't just something wrong with that particular disc.
