If you mean the drive letter has disappered then go here & reassign it.
"Go to Start > Control Panel > Administrative Tools > Computer Management, Disk Management, then right-click the partition whose name you want to change (click in the white area just below the word "Volume") and select "change drive letter and paths."
From here you can add, remove or change drive letters and paths to the partition."
When you get there look around for your burner. It may have a '0' associated with it. Change it back to what it was & problem solved.
I had this disappearing cdrom/dvd/cdrw problem myself when i first started using XP. In my 'get it fixed' routine I flashed my bios, updated my firmware, made sure i wasn't using Roxio software EVER again, and installed the newest 4in1's. Which one helped the most, i think, is a toss up between ditching roxio (for the newest release of Nero), and the 4in1's.