hmmm...if the cdrom is ignoring random disks, it can be a couple things.

The drive is an older drive and cannot read disks that fall under the "high density" group (unlikely, but I dont know the age of the drive). If this is the case, you'll have to replace the drive.

The cd's are scratched or dirty. Grab a soft cloth and clean the cd's. Even if they look clean, clean them anyways. Sometimes there is a film on the cd that creates problems when the drive attempts to read the cd.

The drive is bad. A good indication of this is if you place one of the "non-readable" discs in the drive and reboot, do the pc "see" the disc now? If so, it's time to replace the drive. You can try cleaning the drive with a cd drive cleaner or blow some air into the drive, but honestly, if it's having this type of issue, you're just prolonging the replacement of the drive itself.