Wow, how about a little more information here...
1.) Does your DVD show as a valid drive on your Desktop/Explorer/??? (depending on OS)
2.) Can you open it by software command
before inserting a disc?
3.) Does it spin up after inserting said disc?
4.) Have you installed the drive yourself?
4.1.) Why???
5.) Have you checked if all necessary cables are connected?
5.1.) If you're not quite sure how to do this, don't!!!
Answer these and maybe there will ba an answer - maybe there will be more questions.