Wired Apple extended keyboard a1243 not recognized - Solution in Accessibility Settings.

I found a solution for anyone who is dealing with your wired usb keyboard not being recognized. It happened to me too, about 2 years ago. The keyboard has been sitting in a box since then, til today when I did a little research. Noting helpful here in the forums; But when googling the question, this article from CNET, from 2009, gave the solution https://www.cnet.com/news/mac-keyboard-not-working-mouse-keys-may-be-activated/

Go to System Preferences, then Accessibility, There is a setting for "Mouse Keys"- this setting allows you to "use the keys 7,8,9, U, I, O, J, K, L, M, and '.' (period) to control movement of the mouse pointer and mouse clicking, but other numbers, letters, and keys cannot be used. " (per Cnet article)

Apparently this can become accidentally enabled through an update, migration, syncing or several other ways. It doesn't matter how. you just want it fixed.

When I unchecked the "Mouse Keys" box, the wired Apple Extended Keyboard (a1243) immediately started working again.

Hope this helps.