I actually meant to ask that yesterday as well, my Saturn was freaking out and would only read discs like CDs at one point as well. Turned out the solder on the joints for the modchip had cracked and that was causing the problem.
Since you've got it open, try taping the door sensor closed and putting in a game and playing for awhile with the lid off. If you see it trying to struggle to move the laser on the rails and freezing while playing then you probably just need to relube the rails like other mentioned. Make sure to get the silicon grease like others mentioned, don't use WD40.