Here's the deal. When I unplug my laptop from AC power it continues to run, but does not sense that it is on battery power? Obviously the battery is working, but when I try to change power settings it doesn't let me and says "ON AC POWER" Before this began anytime I would unplug the power the screen would go into a power saving mode. I have a PPO plan so Best buy sent it off and they changed out the hard drive. It still doesn't work so it's sent off again. Any ideas?