Thermal, Serial Recipt Printer won’t show up after reboot

I am providing support to a library that has a Partnertech RP310 receipt printer hooked up via serial (Standard, not Universal). I install the printer, reboot, and the printer vanishes. I have checked the print spooler, and it is running. There is another printer, a network printer, that is working just fine and stays put.

It is XP SP2 on a relatively recent machine. Any clue how to keep it from vanishing?