Nnever had trouble before, now iMac cannot discover keyboard. Have changed batteries. Mouse works normally.
iMac (21.5-inch Mid 2011), OS X Mountain Lion (10.8.2)
What keyboard you're using? The wireless aluminium keyboard?
If you're using the Apple Wireless Keyboard what happens when you press the power button? Does the LED turn ON? Does it flash (indicating that the keyboard is going into the discoverable pairing mode)?
If the LED isn't turning on, then I would pull out the batteries and check for corrosion on the contacts and then verify they are inserted correctly.
If your mouse is still working you could open the Bluetooth preferences and delete the current keyboard pairing, then attempt to re-pair the keyboard by pulling down the Bluetooth pull-down menu and selecting 'Set Up Bluetooth Device'. You'll need to hold the keyboard power button down for several seconds to force the keyboard to turn off, then press the button again and wait for the LED to begin blinking to indicate it is discoverable.
Keyboard not discoverable on iMac
