Seems that Apple had broken the old wired usb apple keyboard on OS X 10.11.4. New wireless Apple keyboard worked fine.

Didn't work at boot time, and didn't work with windows bootcamp, and didn't work when booted from recovery partition, so must be some boot loader problem.

Reseting EPRAM and SMC didn't work.

Restoring from Time Machine back to 10.11.3, with old 10.11 USB installer, seems to only way to fix the problem.

With old 10.11 usb installer, because keyboard didn't work at boot time, and restoring Time Machine backup when booted from 10.11.4 recovery partition broke my fusion drive partition tables. I had to manually destroy fusion drive and delete partitions on hdd and ssd from command line diskutil, and create new fusion drive logical volume and after that it successfully restore backup from Time Machine.

Now keyboard work's fine, but lost 1 day and windows10/bootcamp partition in process.

I have iMac 27" 5k late 2015, but I love using wired keyboard because numpad.

Ran into the same issue after upgrade to 10.11.4. While was on the call with Apple support, it suddenly started working.

Last steps performed -

• System Preferences > Keyboard > Input Source and check/uncheck Show input menu in menu bar
• About This Mac > System Report... > USB

And boom it works. Try and see if it works for you.

I'm having this issue just after updating to 10.11.4 on a late 2015 5k iMac as well. Toggling Input Menu and going into System Report > USB did nothing for me. I can plug in an older style keyboard and get it working, but the newer Apple USB Extended Keyboard will not work. This is at a business with about 30 computers (4 are the late 2015 4k iMacs, one is a late 2015 21" 4k iMac), all now running 10.11.4. This is only happening to one of them.

Resetting SMC, PRAM, switching to another user, and booting into safe mode had no affect.

I did find that plugging the keyboard into a USB hub gets it working again. This is definitely a software bug. I might try rolling back the USB kext to the previous version.

I just upgraded to El Capitan 10.11.4 and I had this problem - It hasn't been a problem since Mavericks where the fix was to plug a USB Extender in between the USB Keyboard and the Mac. Sure enough - plugging in the same USB extension cable makes my keyboard go again.

Looks like the code where this was fixed has reappeared.  See this old thread from 2013: external mac keyboard not working with maverick on macbook air. It is definitely a software issue as exactly the same Mac and Keyboard will work 10.11.3 but won't work on 10.11.4 without the extension cable.

OS X El Capitan: If a USB device isn’t working

Sorry, this is not helpful at all, and seems like you didn't read this thread at all.

Thanks for making us aware of this thread.

iMac, late 2013. El Captian 10.11.4

I am also having this issue... I have tried everything to get it working again. I am lucky that a friend at work had a wireless one lying around to use. I need my USB keyboard to work again. The Apple Support's post is terrible... did they not think we already looked there. I tried everything he said before even looking there.

Apple Support, please don't have an AI bot post something from your site. We need real answers.

floormat212 I agree, the Apple Support repose was terrible.

So, I've confirmed 2 things worked for me:

1) Plugging the keyboard into a USB hub, then the hub into the iMac.

2) Plugging the keyboard into any UBS extension cable, then the cable into the iMac.

The iMac is a 2015 27" Retina. The iMac user wants the numbered, so wireless wasn't an option.

I hope this helps everyone!

Thanks! I saw that on some other posts that the extension cord worked for them too. I will give that one a try and see if that helps.

Gracias amigo.

Welcome, good luck!

So I work with floormat212 and here is what we found:

Using the extension worked immediately. Without the extension we were unable to get the keyboard to respond including caps lock light.

Thinking it might be an issue with the keyboard I brought over a new Apple keyboard and a third party one just in case.

New keyboard works immediately without extension.

After switching back and forth with the non working and working keyboard.... The non working keyboard kicked on and has been functioning since.

Not sure what happened here or why the extension helps.. My best guess was the old keyboards contacts are worn and the extension applies additional pressure on the old usb connection and offers a less worn male usb that goes into the computer. But who knows thought I'd share in the hopes you'll get your keyboards on!    

Additionally if you do not have an extra working keyboard if you go to a local apple store for a genius bar appointment they should have an extra one to use.

I don't believe that contacts has worn out, because restoring 10.11.3 from timemachine has miracle turned my keyboard to back in life, without removing and plugged back the usb socket. And 10.11.4 gived some error in konsole screen when plugged the keyboard on and off from USB port.

I think it's something related that the keyboard also includes usb hub, usb both ends of keyboard. And the computer regonise its a usb hub, but not find it's also keyboard. = driver problem / kernel bootloader (because it's not working at boot time).

Why it starting to work somebody while speaking on apple support, or swapping with different keyboard, I can't explain, because drivers don't fix by they own.

I Have created bug report to apple from https://bugreport.apple.com

And they have asked be to send sysdiagnose and /usr/sbin/systemprofiler xml from my machine, but unlucky I already recovered 10.11.3 back.

I don't think it's contacts either, as it worked fine with a disgustingly beat up keyboard from over 10 years ago, which was the only spare I had to test. I do appreciate the feedback though, thank you!

I'm wondering its related to the particular version of the extended keyboard. Apple has made some subtle changes to the keyboard over the last few years, but I'm not sure if anything internal was changed. What does everyone's keyboard have for the F3 and F4 function keys? For example, they originally had Expose (one big rectangle with 2 smaller quadrilaterals) and Dashboard (circle that looks like a car speedometer), but lated changed them to Mission Control (3 different smaller quadrilaterals) and Launchpad (2 rows of 3 evenly space squares). I can check which one my client has on Wednesday.

I can report the bug to Apple next week when have access to the computer.