More common then not in ps3's these days. Allow me to give you some hints on what it could be and how to fix them one buy one.
Dirty optical lens:
This is where the lens on the laser gets so cloudy from disks,dust, and the list goes on.
Purchase a ps3 cleaning kit you know lose cd's with little burshes on them? This cleans the drive and the lens of the laser.
ok what if that did not work?
Chances are if the cleaning did not take your going to need to new laser. This happends when the ps3 has been used over time face it sony put in a cheap Blue ray. blue rays cost more then the system it self in many cases, so they shoved in a cheap drive.
Now you can purchase these drives over the internet in fact. I seen them go for $69-150 bucks. But lets say you do not want to fix it yourself. I have just the link for you if you just want someone else to repair your unit. www.videogamerepair.com
You alsmo may want to try reseting the unit turn off the unit completly the turn it on while holding down the power button for 10-15 secounds you will hear a beep. A menu will comes up what you want there is to select to set your system back to factory defualts.
Good luck I hope something works of of this for you let me know if you have any questions. Please do not forget to rate the soluton before you leave.