Screen problem Inspiron 17r 7720

i got a new dell inspiron 17r 7720 laptop a couple months ago and everything was working perfectly fine. i was on it one day and out of no where my computer just shut off. i turned it back on to find that the screen would no longer show up. all the lights come on and the fan runs, and i can hook it up to an external screen ( in this case my TV through an HDMI cable) but the screen itself is just black. it looks like the back light for the LCD screen turns on but there is no picture. i have tried shinning a flashlight on the screen and i cannot see any icons, and i have searched the web for days trying to find a solution but cannot find anything helpful. need my computer for all my school work and for work, so please help.