I was recently having issues with the LCD backlight on my Dell XPS M1530 laptop. So I took it to the tech guy who fixed the backlight issue. But, now I get sudden shut downs while I'm working on my laptop. The screen goes white for a second before it shuts off by itself. Could it be an issue with wiring inside which the tech guy messed up? Or maybe the heat? because I notice the shut down when mostly my laptop is resting on a wooden table for about half and hour. Any advise?