Whats Up with My Xbox? is It My Game or the Memory System?

ok so i ordered a copy of halo 3 last month and finally got it. (had to sell my first copy cause i needed the money) and every so often when i go to play it it says cannot read disk. the disk has absolutely no scratches. it also does this with my copy of call of duty modern warfare 2. i cant even play CoD because of it. i dont want to get rid of it just in case i can fix it somehow. what do you think is wrong and how can i fix it? any help is welcome.

Suggestion:

Something Probably Wrong with Your Hard Drive Or the Lenes on Your Xbox