Wireless keyboard stopped working on my iMac

My wireless keyboard stopped working on my iMac. It shows that it is connected, but it won't respond. It's not the batteries, and I tested keyboard on my iPad and it works fine on the iPad, so it is not the keyboard itself.

I also tried to connect a different wireless keyboard to my iMac, but the same thing happens... it shows that it is connected, but it doesn't respond.

When I go preferences > bluetooth, the device shows as connected. I have tried to remove it by highlighting it and clicking the - (minus) , but the - (minus) is not clickable. It is gray.

Also grayed is the box that says 'discoverable'. the box is checked however.

I am at a loss!! Any ideas