Bluetooth Keyboard is not Connecting

I have an iMac running OSX 10.11.6 with a bluetooth keyboard that has not given me any trouble until now. I restarted the computer and now it is in an endless search for the keyboard, one I can only stop by going to the activity monitor and force stopping it. The keyboard has a green indicator light that keeps blinking; not twice, just once, constantly. I am told this means it is paired but the computer cannot find it. Also, the keyboard no longer turns off using the power button; I have to remove the batteries, but it does turn on using the power button.

If you have had this problem before or you think you can help, I would appreciate it.

It is a "Magic Keyboard," the one that came with the desktop.