Believe it or not my local daily paper today has hints on how to deal with this.
1. eject button
2. Cmd-E
3. select the item in Finder & click the eject button next to its name
or
drag the item to the trash
or
hit the F12 key
4. open Disk Utility select the dvd and eject
5. restart Mac holding down the mouse button
If none of these work there's a couple more hints but involve going a little deeper.