The game is most likely on high, it isn't the most graphically pleasing game of course, lol. Did you try comparing it from lowest to highest to make sure it was working? The buttons are just simple execute commands that would change the graphics from lowest to highest.
Also did you try readjusting the volume, gamma and sensitivity sliders in the options menu? That may be causing the game to be mute. Thought I fixed that, lol. I'll have to take a look at it later.