I am unable to activate a dell M782 monitor from the power saving mode after the sleep button on the keyboard was pushed. I have unplugged the power from both the cpu and monitor, powered down both & disconnected the monitor cable. The error message says "monitor in power saving mode use pc to enable". Tough to do when the screen is black! I suspect there is a secret combination of keys that undo this but have no idea which ones to press in what sequence. Help!