late 2006 black macbook display

So I recently got a used late-2006 black macbook on ebay and in the beginning it had a problem of turning on because the screen would flicker when I was trying to press the power button and the sleep light would also flicker and I took it to an apple specialist and they said that their is a problem with the logic board and it had to be replaced. When I replaced the Logic Board, the macbook would turn on perfectly. The sleep light would come on and stay on but the display would not come on and when I try to connect it to an external display, it would not find and connect to the display either. I am not sure what else could be the problem with the Mac