Assuming you can't read a CD in a supposedly working DVD-RW drive, you have one of the following conditions:
1. The CD media itself is defective or dirty
2. The DVD-RW is dirty or defective
Will the drive read DVDs and not CDs? If so, try cleaning the drive. If that fails to fix the problem, then the drive itself is likely defective (there are actually 2 lasers to read media, one for DVDs and the other for CDs).
Good luck!