Hello jannieb and welcome to the forums.
When your drive doesn't recognize media, there are a series of steps you can take...in my mind I call them the usual suspects.
You don't mention which operating system you are using, but I assume its some form of Windows. You can try the Microsoft Fixit tool for optical drives: http://support.microsoft.com/mats/cd_dvd_drive_problems This rarely works.
Then you can move on to the suggestions on this page: http://support.microsoft.com/kb/314060/en-us The second one is the Fixit tool I already mentioned, but the third solution is usually the one that works.