Why won't my PS3 read some blu ray movies and games?

[mr. right]

My ps3 has worked flawlessly for 4 years, but now all of a sudden it stopped reading some bluray movies and games... It still reads AC Brotherhood and some others, but won't read COD Black ops or Mafia 2. I don't understand what happened since I don't leave it running ever and I don't leave it on stand-by either. I would send it in, but I am out of the limited warranty now and I don't have money to send it to be repaired. If there is any advice you can give me, please do. Thanks