So your KDE desktop suddenly ended and logged you out. This is not normal behavior and I have not had this occur with openSUSE 12.1. Now, when you speak of a cd, there are several kinds and it might make a difference. Was it a …
Audio CD, factory or home made (700 MB max or Less)
Data CD and includes MP3’s (700 MB or Less)
Data DVD (4.7 GB or Less)
Movie DVD, home made (4.7 GB or less)
Factory DVD Movie (4.7-6 GB)
Data DL or Home Made Movie (8.5 GB or less)
Any Data Blue Ray disk (25 GB or larger)
Of course you would try the disk again as well as check other disks. If you did a recent update and did not restart KDE, that can do it, but sometime the stars might just be in the wrong alignment for you.