Sounds like you have a bad CD. Either that or you are using a copy of your original.
If the CD is the original, try cleaning it with an optical cleaning cloth. A bit of 92% isopropyl alcohol can be used to get oily smudges off. The alcohol is safe to use on CDs and DVDs.
You can look for damage (or debris spots) by viewing the disk at various angles, against the light. Scratches can sometimes be rubbed out, but USE an optical cloth so as not to damage the surrounding areas. You don’t want to add more damage.
Optical cloths can be found wherever CD/DVD cleaning kits are sold. They are unique in that they are lint-less and non-abrasive.
Anyway, this sounds like your problem. If it were a startup problem, the files on the CD are not actually accessed. MS puts intentional bad sectors on the CD to test/verify you have the original CD.
If it is not present, you are asked to place it in your drive.
Otherwise, everything is already on your HD if you ran the install. There are directory copies available out there, but you will still need the original CD.
Pascal05