my old brick ps3 had same problem, took the thing apart, cleaned it and put it in the oven while i was at it, while it was in the oven, i took the disk drive apart and cleaned the lens with a cotton tip, all done, new thermal paste, cleaned disk drive, and now disks play again and it has never had a YLOD again
but really, i did put my ps3 in the oven and the disk not reading is a common problem, like said, take disk drive out and clean the laser with a cotton bud, even move it a little bit because sometimes the little motor seizes up and thats why the laser wont read, cause it wont move.