In the CD/DVD FAQ at the top of this forum are a couple articles I want you to refer to. First, follow the instructions for running the Dell diagnostics. That will tell us if there is a hardware problem with the drive. The test needs a CD in the drive to run. If you get any errors, let me know.
If all tests pass, then try the article under "code 39 error". Follow the steps carefully and that should restore your drive's ability to read discs.