Hi, a curious problem developed in one of our Samsung Series 9, NP900X3C machines: after about a year (maybe due to heating up?) it won't work on battery any more. This is what happens: as soon as it is unplugged from the mains, Windows 7 starts freezing the video or displaying crazy patterns, and the machine soon hangs. If it is rebooted on battery power, Windows gets stuck halfway on boot. On AC it works normally. I tried updating the bios, video drivers, switching batteries and tinkering with the power settings so they will be the same whether on AC or battery, but to no avail..