horizontal grey lines with black screen appears randomly on my dell laptop

I have been experiencing horizontal grey lines with black screen on my laptop for the past few weeks..The lines randomly appear while booting up or while working and go off if the monitor  is moved..up/down.

sometimes lines appear if i try to move the monitor

kindly help me with this..

My laptop specifications are:

MODEL : dell inspiron 7520

OS: windows 7  home premium 64 bit

Graphic card: AMD radeon hd 7730

my laptop is 2years old