Updated iMac to Yosemite 10.10.5 and USB keyboard stopped working I updated my iMac's OS to Yosemite 10.10.5 and found that the Apple USB keyboard is no longer working.

I tried different USB ports to no result.

I tried using the keyboard on another computer and it works fine.

I tried an Apple Bluetooth keyboard and it works fine.

Would anyone know what I could do to get it working again?
Try this, while it is very basic: https://support.apple.com/kb/PH19094?locale=en_US
Also check what other USB are working (mouse, etc.)
Do a PRAM Reset
Restart >
Command + Option + P + R
holding the keys when the Apple sign doesnt appear yet on the screen,
it restarts and USB ports start working.

You can also try a SMC: https://support.apple.com/en-us/HT201295

I am using a new iMac with El capitan and preferred using my old USB keyboard instead of the elegant wirelerss one. No problems.