It seems to be pretty complex. I have a new battery and new a/c cord. My computer sometimes makes a soft buzzing sound, the screen flickers and then goes dark. Aditionally, with the cord plugged in, sometimes the it switches to battery power and that is when the buzzing begins. I can jiggle the cord and get it to go back to a/c power. When the screen goes dark, the computer switches to standby mode and the screen goes dark. I don;t really understand what is going on. Any help appreciayed!