Not to make you sound dumb or anything but the following questions are just qualifying questions to determine your problem.
Are you sure it's a PSX game?
Is it a copied game?
Are you sure you're pushing the games in fully?
Are the disks dirty or scratched up?
If it's none of those then let me know and i'll make try some other ideas out.......Right now though i'm not sure there could be anything else other than your system being screwed. Well, hopefully we're able to get your system running like new again......without spending a bunch of cash.