What is wrong with a Xbox 360 system if it does not allow you to play Xbox 360 games?

My Xbox 360 system will not allow me to play any of my Xbox 360 video games. Every time I enter one of them, it reads ‘Unplayable Disc’. This applies to them all and from inspecting it, I have not located any major scratches on them or anything really damaging.

DVD drive failure, only covered by the 1 year warranty. You can try cleaning it out with a can of compressed air, it may help a little bit.
Eventually you will need to call xbox support and schedule a repair. If you are no longer covered by the 1 year warranty this may cost $100-$140 to have fixed. BUT when you pay to have it fixed, the 1 year and 3 year warranties start over from the day it leaves the repair center.

E3 2009: Project Natal Xbox 360 Announcement