At first my 360 would freeze and show random letters and numbers on the screen. And after sending it in to get fixed it seems to work just fine.. The only problem is that after an hour or two of playing it says it cannot read the disk. Even though I'v used brand-new disks it keeps giving me this error.

If someone can help me fix this or at least tell me what the problem is I would really appreciate it

How olds the xbox? I've had one or two issues where Ranbow 6 Vegas has stuttered and I had the odd disc read error....

The problem is with rainbow 6 and phantasy star universe... everything else seems just fine

Send it back again, if it's quite new and it's already been fixed once I would ask for a replacement.