The causes of this are:The disk has an abrasion so the files cannot be read. (scratched physicaly)
The disk is dirty (clean it)
The cdrom drive is fail and needs replacing.
Other:you put an upgrade cd in and not a fully fledged recovery disk
Test:Try booting from another bootable disk ie DIFS linked here is an ISO image - made on another machine with working dvd drive ofcourse.
http://tinyurl.com/FJdiags