My friend has a DVD drive on her laptop and it has recently decided to stop playing DVDs for no apparent reason! When I checked the laptop last night it seems that the drive recognises CDs but not DVDs. When I tried to open the CD/DVD-Rom drive it prompts me to try to format the drive, but then tells me that formatting is not possible.
If its working fine with CD's but not recognising DVD's it could be time to buy a new drive. CD's and DVD's are read in different ways by your drive, and this is often the first sign that its knackered.
Nothing lasts forever, and new drives can cost as little as �10 from the right places.
However, without the model number, and error codes i cant be exactley sure what the problem is.