Wireless Keyboard not working

We have quite a few Dell Wireless/Keyboard WK636p that were manufactured in April 2018. After we installed them, a few months later, the keyboards become complete unresponsive. The mouse works just fine, but we get nothing from keyboard. We have replaced batteries with brand new ones and still nothing. There are no lights on the keyboard at all. It doesn't matter which desktop they are plugged into, the keyboard still does not work. We are able to install a new wireless keyboard/mouse on the desktop and they work. I have looked online and have not found any help.