Hello!
If you still some kind of Windows box to test it on, try that, but it's starting to sound like the drive itself might be defective. It's rare that the CD-RW part of a DVD is defective, but not impossible.
Now I HAVE seen CD/DVD drives fail they other way around - CDs play and burn fine, but DVDs won't read or burn. Mine are like that, but the PC is a Gateway, and the front of the drives are curved - otherwise, I'd replace them.
Fortunately, I have a Sony external that works like a champ. It even lets you hook up an analog/digital camera or VCR and burns things on a DVD...
73 DE N4RPS
Rob