I hadn't rebooted my Mac in a while and it was starting to be super sluggish. I had it docked, so MagSafe, a USB cable for the keyboard & mouse etc, and display port. After rebooting it displayed on both screens (despite being a closed clamshell). I opened and closed the screen to get it to recognise it should be only on the big screen, and that's when I noticed it: 'No battery available'. Power Source: 'Power adapter' Here's the thing: I unplug the MagSafe and it still operates. However when I unplug everything and lift the lid, nothing happens at all. The Mac is good as dead. Plug everything back in, and it's as if nothing happened. Still 'No battery available' though. Any help? Thanks! EDIT: A careful shut-down and then un-docked switch-on of the Mac has resolved the problem it seems!