That's the voicemail key, that allows the voicemail to work (a hardware licensing key, per se). It must be attached to the parallel port, and doesn't need anything attached to it.

What's the background on this PC? Was it in service at one time? Did the PC or other hardware get changed out between the time it was working and now?

If it has been sitting without power for a couple years, my guess is that the BIOS has defaulted, and needs to be fixed so the voice board(s) will work. There are certain settings that need to be made in the BIOS, in order for the board(s) to work correctly. It sounds to me like Voicemail can't find the voice board(s). Assuming the boards ARE physically installed in the PC, then the BIOS settings could very likely be the problem.

Justin