Apple USB keyboard troubles during startup

We've been having this problem too -- 27-inch iMac with retina display, using OSX (10.11.3), the Apple aluminum USB keyboard, new wireless Magic Mouse.

On startup, the Apple aluminum USB keyboard doesn't work. Been happening for months.

Oddly enough, when we unplug this keyboard and insert an older keyboard (Mac or IceKey), the old keyboard works. Wait a few minutes and switch out for the newer keyboard and then it works fine. Until the next startup.

We tried a couple of other tricks learned via Google searches -- using a USB extension cord, unplugging/replugging, zapping PRAM/SMC. No help.

Today, I read a post about the computer prioritizing the bluetooth devices, so we tried restarting with the wireless mouse turned off. The keyboard worked! Then we turned on the mouse and everything was fine.

So maybe it is a bluetooth issue -- that once it finds the mouse, it expects to find a keyboard and when it doesn't, it just doesn't recognize the keyboard. Completely novice guess! We have a second iMac with the same configuration except a wireless keyboard and (knock on wood) have never had a problem.

Hope someone from Apple is monitoring and can add this to the list of glitches.

Good luck!

The other thing I read about... was about to try when turning the mouse off worked... was bluetooth interference.

From Apple: Other wireless devices that operate in the 2.4 GHz or 5 GHz bandwidth (microwave transmitters, wireless cameras, baby monitors, a neighbor's Wi-Fi device) can cause interference with Wi-Fi or bluetoothconnections.

Maybe something else is screwing with the bluetooth?

Good luck.

Concerning USB keyboard issues: I just experienced the same issue during a cold start up. The keyboard was not responding. I restarted again, the keyboard did not respond. I unplugged the USB cable from the back of the iMac and plugged it into another USB port, same issue. I unplugged the USB cable and plugged it into my Belkin hub and it works now.

Here is my conclusion: I hope this is not the case, but there is a possibility that the malfunction is a hardware issue with the USB ports on the back of the computer. The less expensive scenario is the keyboard itself.

I will try to another test and directly plug the keyboard back into the computer to see if it happens again during a restart.