As mentioned before, try cleaning the lense with something alcohol based (I use aftershave
It also helps to re-grease the laser sled & rails, as this allows the laser to move smoothly to the correct position.
Also make sure the inside of the drive is SPOTLESS - dust/dirt build-up on any moving parts will lower performance, and at the worst cause you problems with media.
Yes you may have a bad laser, I bought one stating **NEW**, but when I received it, it obviously wasn't. It didn't even work! I fix a lot of consoles including Xbox 360's which are well known for their crappy DVDROMs and quality of build in general. Sony have a good reputation which is shown by the PS3's rock solid performance & reliability.