I've had a Dell XPS laptop for about two years and four months now and I have been having this issue for a long time. The laptop just shuts off without warning--hard down. Once it shuts off, I cannot power it back on unless I plug the AC power in. The power literally just needs to be plugged in for a second and then I can disconnect it and the laptop will turn back on. The battery is not the issue and this is my second battery as I had replaced it a while back, thinking it was the issue. I had the motherboard replaced a while back and also the module where the plug connects to. This is VERY frustrating as if I am in a car or mobile, I cannot turn the laptop back on until I get somewhere that I can plug it back in. I have tried updating drivers, BIOS and many other items without success. Feeling hopeless! Hope someone has a solution.