MacBook pro screen wont turn on mechine turns on but front sleep light is dim

So I was just browsing on chrome on my MacBook pro and suddenly the screen froze and from the top of the screen it started to get dim and came down right to the center of the screen and then another black shade ontop of that came down and stopped in the middle it did this until the top half was completely dark but the bottom half is ok and nothing happend oh by the way I was just on Facebook I wasn't on a website that was harmful to the Mac so any ways I then I held the power button until it turns off thinking it would work normaly but it didnt, when I turned it on I heard the fan turn really fast and then it slowed down and the front sleep light came on and it stayed like that, i could also hear the hard drive spinning inside I closed it and the sleep light is on it but now it brighter and it's not even going dark and bright like its supposed to do when it's sleeping. Can someone please help?