AVG AT, AVG... or failing that, Avast. But AVG first.
I expect backup CDs to fail. CD-Rs are a fickle medium, prone to failure after 2-5 years, depending on brand and environmental conditions. Its best to replace backup CDs once a year or so... Of course, even better is a backup USB hard drive (really an IDE drive placed into a $20 (check deal listing sites periodically) aluminum enclosure since "external" drives are ridiculously overpriced) that is only on when you copy backups to it, then you put it in static shielding for storage.
That was way too many nested remarks... oh well.