Sceen keeps flickering then goes black! =[

Hello,
Im just wondering if u can help me, my laptop goes on fine till the password screen comes up it starts flickering but i manage to enter the password and it works fine loads properly and everything, give it a few mins and it flickers more then screen goes duller then just goes black! I shut the lid for a few seconds then it comes around but continues to do the flickering and goes black over and over again! When screen it black i can kind of see somethings on screen if i shine a light onto it! Please can someone help me!