The Lightscribe drive doesn't appear in the Device Manager or in the BIOS.
I've had a look inside. The PC has one HD and two optical drives - Lightscribe and DVD-ROM. There are 4 SATA connectors (SATA0,1,2,3). The manual says to use SATA0 and SATA1 first. The HD and DVD-ROM are connected to these, respectively, and both are working fine. The Lightscribe drive is connected to SATA3, as directed in the user manual; SATA2 is reserved for a second HD. I've checked the connectors and nothing is loose or bent.
I'm tempted to swap the Lightscribe and DVD-ROM sata connectors but am a bit worried that I might end up with them both out.