Not sure if my screen is broke or my lap top

I have a Toshiba Satellite :655D-S5093. I replaced the screen about 9 months ago. Today while I was online, the display suddenly showed some lines. I shut down the computer but when I tried to put it back on, black screen. I can hear the fan running, so it powers up , just no display Also no "lights" on my caps lock or num lock key. I tried hooking it up to external moniter and hitting FN + F5 but it does not come on... I went to geek squad in best buy and they said probably the screen , but how can they tell without "opening up the computer. If it was just the screen why wouldn't the external monitor work? help please!!