Pairing magic keyboard keeps failing

Last week I was charging my magic keyboard and when I unplugged it, it would no longer connect wirelessly to my IMac. I can use the keyboard if I have it connected with a USB cord-but when I try to pair to wirelessly to my IMac it keeps saying pairing failed. I have removed the keyboard and tried to re-add it with no luck. When I pull the keyboard up in the bluetooth setting I can see it connecting for a second then disconnecting on and off.