Finally, I booted into the BIOS (that was what had changed, after all) by rebooting the computer and immediately pressing the F2 key when the computer first began to start up. That took me to the blue BIOS screen, at which point I found that the WiFi – as well as the web cam – had been disabled. Since that was at a more base level than even the operating system, this explained why Windows didn’t think the wireless card was there. So I enabled the wireless (and the web cam), restarted the computer, and all is well now.