Have you changed any hardware recently? If so, verify that both your power and data cables are properly connected to the optical drive and the motherboard. If connected properly, then (in this case) you have a Windows issue or a defective optical drive.
If you are using Windows 7, go here and run the FixIt for this problem:http://support.microsoft.com/kb/982116
If that fails to solve the problem, it is likely time to get a new drive.