Laptop totally black screen

I have a Samsung NP350V5C-A03IN laptop.When I power it on, the screen shows nothing at all, even no faint light.But some time it starts up normally.My laptop battery is not working so I use it on direct adaptor charging. Some time the laptop boot up with dead screen and automatically shut down itself and does not boot up even it is not unpluged. What should I do?Please help me.