On my PS3, the ejection mechanism skipped a gear because my 2 year old pushed too hard to put a disc in. The result looked like it accepted the disc but would never play it. Then it would sit there until you ejected it. I was 3 months out of warranty and didn't like the $150 repair option with a 90 day warranty for the repair, so I took it apart, inserted a disc, watched it not take it in all the way, then moved the ejection mechanism back one tooth on both sides. Problem solved.
Answer to: Why won't my PS3 read discs?