Quick question about waking up from sleep

[brewser]

I have two 20" imac's same models core 2 duo's. one machine i can wake up from sleep by moving the mouse. The other won't wake up unless I hit a key on the keyboard. Why can't I just wake up the computer with the mouse on the other one? I have looked over different settings but don't see anything on this. Both the keyboards and mice are apple bluetooth.
Thanks for the advice.

 

[rainydays]

Check under System Preferences->Bluetooth->Settings and make sure "Allow Bluetooth devices to wake this computer" is enabled.