The dvd drives tend to have issues. make sure your discs are clean and not scratched. If they are badly scratched use an automotive cleaner / wax to gently polish out any scratches.

if the DVD drive is still not working the drive is replaceable. replacement drives are readily available on ebay, do an internet search on how to swap the drive.

If you are not familiar with opening a computer case and replacing components in it I would let someone who is familiar with the process do it for you.

Hope that helps