No Printers or Devices in "Show Printer and Devices" (but available!)

I don't see any Devices, or more specifically, any Printers, in "Show Devices and Printers". All the printers are there if I use an application like MS-Word and want to print, but there's nothing in the display. If I bring up "Show Devices and Printers", it spends a long time (a minute) searching as the progress bar slowly moves across, then it comes up blank. Everything else appears...