Sorry for not getting back to this in a more timely manner. The computer in question is my office workstation, and eventually I need to get some work done for my boss regardless of whether I can print. But not being able to print has been a serious headache.
Thanks to all who made suggestions here. I tried it all, and tried some stuff that made me wonder if I was destroying my machine while doing it. Fortunately, I didn't do permanent damage to my setup.
Anyway, it turns out that printing just started working again after the machine was rebooted. So I think I'm good now. (In case you are wondering why I didn't do that much earlier, my machine sometimes acts as a light-duty server, and opportunities to reboot are often very limited.) Thanks again to everyone who tried to help.