|This is likely two or more of the following:|
1.) When you burn your WIndows XP disc, make sure you burn at the LOWEST SPEED. Burn it at 16x and NOT higher than that. The disc your may have or have not have is probably burned at 24x or greater and thus, the drive can not read the data on it.
2.) The Windows XP disc is probably scratched or warped. If it is, then its less likely the dvd drive is going to read the disc, and I suggest to recreate a XP cd.
3.) Leave your windows xp in a cd case. Leaving it on a desk or on the carpet, etc will get dirty, scratches, etc.
Good luck and BACK UP your data and then format the computer and lastly, install a fresh copy of Windows XP.