Q: Apple wireless keyboard stopped working after latest Mavericks update

Putting my two cents in here - worked for me as well! Hold down the power button throughout is indeed the secret.

seanboy1946 thank you - you are absolutely correct - in may case - a nearby iPad was connected so MBA could not. 3 batteries changes, and 10 minutes later - after checking other nearby Macs, I checked the very nearby iPad - and it was happily connected to keyboard.  Once Bluetooth was turned OFF on the IPAD - bingo - happiness is a working bt keyboard. Sometimes it’s the simple things.

Thanks!!! Hoping down the power button on the trackpad worked for me, too!

This worked for me just fine:

https://discussions.apple.com/thread/5496838

This post is a bit old but after searching for ages online I thought I'd share what worked for me, hopefully this will help others in future:

If your keyboard/mouse will not connect via Bluetooth, or appears completely unresponsive, then the following instructions may help you resolve the issue.

NB: This trick works especially on the original Bluetooth Wireless keyboards, mice and trackpads. New keyboards and trackpads were released in late 2015 which do not have removable batteries. This may not work for those devices. Please let me know if it does so I can update this.

1. Switch off the keyboard by holding down the power button for at least 3 seconds
2. Click the Bluetooth icon in the menu bar
3. Click on “Set Up Bluetooth Device” or “Open Bluetooth Preferences”
4. Turn on the keyboard by holding down the power button, BUT DO NOT LET GO OF THE POWER BUTTON. It must be kept held down through the entire process.
5. The Setup Assistant will find the keyboard, so click the name of the keyboard, and then click on “Continue”. Make sure you are still holding the power button down.
6. You will be prompted for the Pairing Code. You can now release the power button, type the pairing code on the keyboard and then press return. There will be a slight delay whilst the pairing completes (a few seconds)
7. The keyboard will now be Paired.

So just to clarify, the trick is to continually HOLD DOWN THE POWER BUTTON.

I realize this is an older thread, but since I found it looking for help, I'll assume others will as well. My issue ended up being REALLY stupid, which is why I'm sharing it.

I recently purchased the newer Apple TV (4th gen) and had paired my older, but still working, Apple Bluetooth keyboard with the Apple TV to aid in typing in all the passwords I needed. Once I was done, I'm almost certain that I disconnected the keyboard from the TV and re-paired it with my Mac. As a matter of fact, weeks have passed without any issue... the keyboard was paired with my Mac and I merrily worked away.

Last night, a circuit breaker popped and my Mac lost power in the process. It was late at night so I didn't bother powering it back up. I just flipped the circuit breaker and went to bed. This morning, I powered up the Mac, but could not type in my password. Weird. I changed batteries on the keyboard. Still no joy. I connected a USB keyboard and logged into my Mac. I made several attempts to connect to the keyboard through Bluetooth settings, deleting bluetooth.plist, and rebooting, but nothing worked. My Mac could see the keyboard, and attempted to pair with it, but the handshake would never complete.

Then I wandered into my living room and noticed my TV was on. I had not turned it on. The new Apple TV will automatically turn on the TV if it receives any input (which is really cool), but the remote was sitting on a shelf untouched. Then it hit me. The keyboard, after losing connection to the Mac, had set itself as available and the Apple TV happily grabbed a hold of it. I confirmed my suspicion by going into the Settings page on the Apple TV and there it was... Apple Keyboard = Connected.

I re-disconnected the keyboard from the Apple TV, went back to my computer, and immediately made a successful pairing attempted. It's a weird story, and probably not one that a lot of people will experience, but the bottom line is to make sure your keyboard is not paired with something else.

Thanks justintb, holding the power button on my older model keyboard did the trick.

It is weird I had this problem, as I have had the keyboard paired with the computer for months. It just stopped connecting.