Macbook Pro A1398 Black Screen & Won't Log In

So I work at a electronic repair shop, and a MacBook Pro A1398 was brought it by a friend who stated the screen remains black when she turns it on, but she can hear the sound of it starting up. I slaved in a monitor to the laptop, and attempted to log in to the laptop, but when I did so it would turn black (leaving the loading progress bar on there) and freeze. I've tried a multitude of problems, including but not limited to: Resetting NVRAM, starting in safe mode, and starting with Shift+Ctrl+Option. Meanwhile, the original screen has remained black, only to emit a glow (meaning a lit black screen.) Can anyone give me any advice or clue into this? Is this a un-rare problem? She bought it on September 14th of last year, 2015. Any help would be much appreciated, since replacing the screen would be costly and wouldn't necessarily fix the log in problem.

NOTE: I am unable to remove the bottom and momentarily take out the battery or RAM, for it requires a pentalobe driver bit that even my shopt doesn't have.