I had exactly the same issue - Apple USB keyboard with numeric pad no longer works (caps lock does not light either) with my late 2013 iMac.

I found a solution that may work for others: I plugged my keyboard into a Windows PC (Win 7, but probably not relevant) to see if it was dead and it was detected, but failed to install correctly, not surprisingly. This confirmed the keyboard still worked as caps lock would light. To my surprise when I plugged it back into the Mac it worked fine! No idea why, but it may be worth trying.

Same issue here on my new Macbook Pro 13 retina. I tried all of the troubleshooting advice with no success. Verified keyboard works fine (no mechanical issues). I then plugged my Apple USB keyboard into the USB slot on the back of my Apple 27" monitor and it works fine, now.

Not an ideal fix, but good enough for now.

Just upgraded to Yosemite on my iMac and  my wired keyboard seems to behave as if the right arrow is stuck. Whenever I open up the Applications folder, it scrolls through all the applications and won't stop. When I click on the top bar menu options in any applications, it scrolls through al the options and won't stop. Had to unplug the keyboard but cannot find a resolution besides buying a wireless keyboard.

I found a solution similar to what others have pointed out.  The issue seems to be that within the keyboard itself something needs to be "switched on" for lack of a better word (needed to "flip a bit?")

I found that by connecting my keyboard to an old Macbook Pro I have hanging around and getting THAT computer to recognize the keyboard first, when I then plugged the same keyboard back into my 2014 iMac seconds later it was immediately discovered

I am having the same problem.  I use the wired keyboard as I need the number pad for work.  I installed Yosemite yesterday with my Apple usb keyboard plugged in, now when I go to use the computer the keyboard doesn't work at all.  I tried unplugging it and plugging it back in, nothing.  I don't have another device to plug the keyboard in to in order to "activate" it... any other suggestions?  I just purchased it less than a month ago too, so to have it suddenly not work with the new OS is not acceptable to me.  I am new to Mac and having it's own peripherals not work seems ridiculous. 

I also found that if you plug a USB device (I used a memory stick) into a USB port on the keyboard while it is plugged into the Mac the keyboard starts working again after a few seconds. Worth a try!

Ah, yes, I always forget about those two usb ports.  Thank you!  I plugged my iPhone into the keyboard and that "activated" the usb keyboard.

This has been a long-time issue with my MacBook Pro, Thunderbolt Displays (I have two), and wired keyboards (I have two). Apple has been unable to solve the issue after repeated calls over the years, but then it would start working after some fiddling and I'd let it be. Installing Yosemite seems to have compounded the issue, but I'm delighted to report that putting a USB device (a memory stick in my case) into one of the ports on the keyboard itself miraculously caused the keyboard to start responding. It's obviously some kind of issue with OS X's detection and registering of USB devices. I hope this trick works consistently. Thanks @awhit613!

Yeah, I tried the same thing before the "plug the keyboard into another Mac" trick but the USB stick wasn't recognized, nothing happened.  I too have had a few situations in which my iMac running Mavericks "lost" the wired keyboard, usually unplugging it from the USB port and plugging it back in did the trick but  that didn't work for me after installing Yosemite either.  For some reason the keyboard isn't "discoverable" so it's invisible to the operating system until some  unknown bit gets flipped in the right direction :-)

How frustrating. I've tried the "USB memory stick into the Apple keyboard" approach and the "Apple keyboard into a USB hub" trick. Still nothing. It's definitely something to do with Yosemite as I get the same locked-into-scrolling keyboard on both my iMac and MacBook Pro (whereas prior to updating, the keyboard worked perfectly).

Since installing Yosemite, the keyboard shortcuts ⌘1 thru ⌘9 do not work upon initial Safari launch. I must first access the shortcut via the Menu. Then things work normally. Well, for an indeterminate amount of time (usually an hour or two). After that, I must (re)access the Menu shortcut again to get the keyboard shortcuts to work.

AFAIK, this keyboard-shortcut issue is only with Safari.

FWIW, I have wired keyboard.

P.S. My workaround solution was to re assign the shortcuts with http://nulana.com/shortcuts/. Works great!

Hi,

when all all else fails try this (courtesy of an Apple Chat):

OS X Yosemite: Reset your computer’s PRAM

 

 

 

 

If your Mac doesn’t seem to be remembering your speaker volume, display resolution, or the disk it should be using during startup, you may need to reset your computer’s PRAM.

Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.

Important:    To print these instructions, click the Share button in the Help window, then choose Print.

 

1. Choose Apple menu > Shut Down.
2. Locate the following keys on the keyboard: Option, Command (⌘), P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on your Mac.
4. Immediately press and hold the Option-Command-P-R keys. You must press this key combination before the gray screen appears.Continue holding the keys down until your Mac restarts, and you hear the startup sound for the second time.
5. Release the keys.

After resetting your computer’s PRAM, you may need to update your speaker volume, display resolution, and startup disk preferences. For more information about PRAM, see the Apple Support article About NVRAM and PRAM.