Could be that your DVD drive connection is faulty; you can open up your PC and make sure the cables hooked up to it is correctly connected.
Worst case scenario, just buy a new DVD-RW drive and try it out (assuming nothing else is affected). If that don't work, then something is really wrong
Last resort would be either buy a new DVD-RW drive or reformat the whole system to make sure it's not a software issue.
That's all I can think about right now, wait for some other users' suggestions to make sure I'm on the correct line.