Help! Bluetooth vanished!


I installed the latest system update this morning, from Software Update. It was supposed to be able to adjust the brightness of the sleep light. When I restarted, all traces of Bluetooth had vanished from my computer and I seem unable to reinstall it, even from backups. It keeps saying I do not have a Bluetooth module installed. Any clues? (So glad I never threw away the old usb keyboard and mouse)
Update: I tried something I read on another site, where you disconnect everything from the computer, cntrl-shift-opt + Power for 10 secs, etc, etc, then boot. The bluetooth keyboard and mouse now work, but Bluetooth isn't on the Systems Prefs panel and it's vanished from the menu bar, so I can't adjust or change anything.