So, it happened that a friend of mine turned off Bluetooth on her Mac mini, and then turned it off for the evening. When she got up the next morning, her Bluetooth keyboard was on, as per usual, but she couldn’t log in on start up, as her Mac did not see her keyboard.
She was worried that she’d have to go borrow or buy a wired keyboard, plug it in, and enter her password, then turn Bluetooth on again to make her wireless keyboard work again.
Luckily, that’s not what had to happen. Here’s how we solved it.
When you turn on your Mac, it searches for a connected keyboard and/or mouse. If it can’t find any, it will ask you to connect them yourself, even if it’s a Bluetooth device.
The trick here is to get your Mac to forget that there are devices connected, so that it asks to pair the keyboard and mouse again.
All we needed to do was disconnect the wireless mouse, which has a little USB dongle that it connects to, and turn off the Bluetooth keyboard itself. Then we shut down the Mac mini all the way (restarts hadn’t worked), and then pressed the power button to get it to turn on.
As soon as we did all of that, boom, her Mac Mini asked her to connect the Bluetooth keyboard, then the wireless mouse. Once she powered up the keyboard, she was able to enter her password and be on her merry way. I asked her not to turn off Bluetooth before she shut the computer down again, just in case.