superdrive does not recognize the inserted CD-RW disk
When I insert a CD-RW blank disk into the drive the IMac does not recognize it.
iMac, iOS 6, Vertical line on screen
Try a different brand and retest. If that does not work, go to your local office supply store and get a CD/DVD cleaning kit and use that to clean the drive. If the drive still doesn't work it may be failing.