Magic Keyboard doesnt stop blinking not allowing to login the password.

After changing the batteries, the magic keyboard doesnt stop blinking, not allowing to login the password at the Imac. I thought the Keyboard was broken, so I tried to pair it whith the macbook pro and it was OK. I unpaired from the macbook and tried rebboting the sistem , holding the on/off button of the keyboard, not holding, turnning on before and after the reboot and nothing happened. The keyboard, remains blinking searching for the computer. Whar should I do to gain access to the imac again?