Why did my USB keyboard stop working?

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.

Very fair points! The main reason I went to suspecting contacts was the fact the extension fixes the issue immediately. Yesterday my curiosity got the best of me and I smashed a spare USB extender to find there is nothing in there controller wise just wired to the contacts. After ripping open a apple wired keyboard I found the following usb controller http://media.digikey.com/pdf/Data%20Sheets/Cypress%20PDFs/CY7C63310,%20638xx,%20 639xx.pdf built into the keyboard and wonder if the update is affecting the usb controller inside the keyboard thats connected while updating? Still can't wrap my head around the extension piece or why several disconnects and reconnects helped.

I have MacBook Air (early 2015). Just upgraded to OS X El Capitan (10.11.5) - the external USB keyboard did not work and was not found in the system report. Tried resetting etc and still nothing. Plugged into extension cable and worked instantly. Tried plugging back in on its own and same issue not picked up. Just thought I'd post here as this issue is still occurring.

The latest upgrade to El Capitan 10.11.5 has fixed this issue for me - I have removed the USB Extender in between the USB Keyboard and my iMac 5K and the keyboard now works (working as I type).

Strange - as 10.11.5 fixed this issue on my iMac 5K late 2014.

Hi mate,

I've tried many a remedy for this but found the following sequence worked:

1. With computer on, disconnect USB keyboard (if not already as it's not working, haha)
2. Turn off Bluetooth
3. Plus USB keyboard back in and test (for, this worked)
4. Turn Bluetooth back on

Cheers,

Jamie

This did the trick for me! Thanks so much for posting it.

I just updated to Sierra in December and found that only using the USB extension cable allows my USB mice to work. I can't believe that Apple hasn't resolved his yet. Thanks for sharing this temporary solution.