Hallo Tom,
A number of issues can cause this, but first - how is the CD you are trying to burn going to be used? If it is to make back-up copies then I'd suggest avoiding CD (particularly RW) altogether. Rewritable discs can be fairly unreliable and the fact that your pc is not recognizing it could suggest it is a disc problem. Another possibility is that the disc has been used before and needs erasing - or that the optical drive's lens may need cleaning. Have you tried using different discs? Cheers, Ric.