My screen goes dark when I pull out my power cord

Hey

I just bought a new laptop named Studio 17 from Dell. I've got a problem when I pull out out the power cord to the laptop. The problem is that the screen becomes so dark that I can't see anything, so I have to restart my computer every time. And when my power cord isn't connected to my computer, it takes ages for it to even start windows. So basicly I can't use my laptop without having the power cord connected, which basicly ruins the whole idea of me even buying a laptop ;) so is there any idea of what could be the problem? maybe I've overlooked some settings?