hmm.....check in device manager and make sure it is listed - start > settings > control panel > system > hardware > device manager, see if it is listed there and if it has any red x or yellow ! or ? on it..if it does there's a problem recognizing the drive or it has a problem working correctly...if not, try finding the driver for your drive on the manufacturer's website. although if this is winxp it may not need a specific driver, perhaps even in win2k.
the easiest thing to do )and perhaps most effective) is uninstall that device in device manager, then reboot and it should reinstall itself. probably without any user intervention also. then check in nero and wavelab.
questions...what OS? what kind of burner? it used to work before, right?
have you installed any hardware/software recently or since the last time you used it?