Playstation 3 Disk Read Help?

I know a lot of people have had similar problems, but im needed a good answer on exactly what to do. My PS3 seems to hate reading certain discs of mine, like Darksiders or Modern Warfare 2, but it reads games like Infamous 2 and COD: Black Ops just fine, I always end up having to put a certain game in so my PS3 will read it, THEN I can put in whatever game I want (like MW2) and it finally reads it just fine. But it wont read it unless i put certain discs in. I would really like some help on the subject! Thanks. :)