There are several things it could be. The system is booting up ok, just not reading the games? You might want to firsttry cleaning off the discs with a soft cloth, wiping from the center of the disc and going toward the edge to get rid of any dust or fingerprints.
One other possibility is the lens inside is dirty- this can be taken care of using a DVD player cleaning kit or (if feeling brave) instructions can be found on the web about taking the top off and cleaning the lens yourself (not personally recommended though).
If neither of these solutions work things might be a bit more serious- I would give Sony's tech support a call at 1-800-345-7669.
(3 hrs 14 min)