I have had the same issue in the past and it turned out to be that somehow the media device for these applications got changed. In xine, go to settings and then to media. Check and make sure that the correct /dev/ file is point to your CD/DVD drive. In most cases, it will say /dev/cdrom, but you may have to look in your etc/fstab file and see what your system notes your drive as (i.e. /dev/hda or /dev/hdb, as will be the case if you are using SATA hard drives.)
Do this with the settings of any media player that will not find your CD/DVD device.
Hope this helps