My MacBook Air has problems finding my wireless keyboard. It is paired, but not seen. I have to go through the whole rigmarole of adding a new device to make it visible. Why?
Sometimes Bluetooth preferences lets me connect; sometimes not.
My Keyboard isn't a favourite! Solving this should be easy—just use Bluetooth panel in System Preferences.
There's an obvious button to press in Tiger; but on Leopard it's hidden.
Solution
Open Bluetooth Preferences ...
Select your device (Keyboard or whatever).
For an immediate fix select Connect from the settings menu.
For something longer-lasting, select Show More Info
The trick: From the settings menu (which has now changed) select Add to Favorites. You're done.
Sometimes it shows connected but still no keystrokes appear: Disconnect and then Connect using the settings menu.