dell vostro 1510 screen flickring problem

screen of my dell vostro 1510 was flickering i called at call center they guided me to do all the test.. i did all the test including 30 minutes test of safe mode , i attached my laptop with a dell led and screen was not flickering there and in safe mode it was flickering there please guide me whether i need to check the cable of the screen or i need to replace the screen with the new one  ? please guide me