It doesn't show up at all, or is it showing up as a CDrom? Try this, put a CD in the drive and leave it in while you reboot. I had a problem with all three of my drives in the beginning but if i left CD's in the drive XP would pick them up.
Get your newest motherboard bios flashed in.
Get your newest DVD firmware flash.
Get the newest 4in1's installed.
(maybe) mini-port drivers can help.
Install an ASPI-layer.
did you do any of the possible fixes i listed earlier? If not, give those a try. If you have, list some system specs for us - m/b, type of drive, how it's set up on the IDE channel (master or slave and to what).
It's my guess that it's Nero causing the problem. There's some registry cleaning you need to do to undo the damage. Use the search function above right, and type in "Nero." A lot of folks have experienced what you're going through and the fix is here so give the search a go and see what you can find.
I thought the newest version of Nero fixed it's earlier problems. Let me know how you get on with the registry thing. If it's not that then i'm not sure what it could be, but i'll definantly try to help.