If they are done though a backup program the File Type may be unreadable by XP.
Though the more likely option is either the CD's themselves have been left so long that they have degraded and are now unusable through either long term storage or Poor Storage. If Recordable Optical Drives are left in direct sunlight the Dye degrades and becomes unreadable through UV Decay. There is also the possibility to marks or scratches on the Recordable Disc's rendering them unreadable.
Or the actual Optical Drive can not read this dye type. The Dyes used on Recordable Optical disc's has changed dramatically over the years from a Gold Color to Blue it is possible that if this is an Old Dye Type the Optical Drive can not read the Disc.
Last option is that the Optical Drive itself is not working have you tried different Disc's in this drive to see if it works?
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