Suddenly Apple Wired Keyboard not working

I resolved my issue by following the SMC Reset instructions here.

Basically unplug everything, power down the mac, hold the power button for 5 seconds. Once the system has rebooted then reattached all peripherals. Then my keyboard started working again.

Kieran

This is what solved it for me:

Eventually I found this thread on the Apple website, and followed the rather bizarre advice of adding a USB extension cable between the keyboard and the Mac (luckily the keyboard comes packaged with one). Bingo! Keyboard fine, mouse plugged into it also fine.

^{http://www.zigpress.com/2014/12/30/has-your-apple-mac-external-usb-keyboard-stopped-working/}

I think the problem is that the keyboard draws so little current that it won´t wake the port if you have the Apple keyboard with a usb hub.

Just stick a usb memorystick in the keyboard and re-insert the cable. If it works then just remove the memorystick or what ever you put in (doesn´t matter what).

Just tried adding a usb memory stick fix, and it worked. I can't believe I am having to do this, why can't apple recognise that it is a problem.

I just had this on a box-fresh macbook pro. Sigh. This was the only thing that worked for me:

To reset the SMC:

1. Shut down the computer. Plug in the MagSafe or USB-C power adapter to a power source and to your computer.
2. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
3. Release all the keys and the power button at the same time.
4. Press the power button to turn on the computer.

Source: http://support.apple.com/en-us/HT201295

Update

Actually, using the USB extension lead is all that works now. Reproducibly weird.