Cannot adjust brightness; it's getting weird.

So for the past day, my 13" Macbook has been acting very strange. When I first boot it up, the screen is at the brightest setting; however, when I attempt to change it, the little brightness sun thing says that there is no brightness. When I then shut my computer (not turn it off, just close it) and open it again, everything is dark and it's at zero brightness. This is getting pretty annoying. Does anyone have any idea what could be causing this or how I could fix it? If so I would be very thankful and overjoyed!