I've searched and this seems a different problem to those discussed. MacBook Air 2010 running Mountain Lion. When plugged into power it works fine. No problems When on battery power it boots up but once on desktop it lasts about 60 seconds before the screen goes dark. It isn't off as there is a dull light coming from the screen but nothing is visible. Then after a few minutes the fans kick in. If I press the power button once nothing. If i hold it down the screen flashes and it turns off and screen goes completely black. Off. Sometimes if I try to restart it produces a deep beep with a gap inbetween. It's not just 1 to 5 beeps for bad RAM etc, its just beep, gap, beep, gap and continues. I counted upto 30 beeps before I held down the power to turn off laptop. It's a worry. Any ideas? Thanks guys.