|"I saved a file to my CD and the files already on that CD are no longer listed. How can I recover those files?"|
The other files are probably still there unless you deleted them yourself.
Try cleaning the laser lens on the drive.
If this is a desktop computer, use a laser lens cleaning CD. If you don't have one, most places that sell CDs and DVDs have them, and even some "dollar" stores have them for a buck or two.
If this is a laptop, you could do that, or eject the tray, and with no disk on it, wipe off the obvious laser lens with a tissue or a soft cloth.
A burned CD that was made in one drive model may not read properly in another drive model, especially if it's other than a CD-R or DVD-R disk.
Try reading the CD in a different drive.