MInecraft Not functioning, won't quit

When in single player mode, Fps started at 30, then was shifting between 0 and 15, and the game wasn't really running at all (obv.). When I attempted to teleport, the new location wouldn't load, so I tried to quit. The window turned black and wouldn't quit, even when I tried to log out of the computer. However, the launcher could still open another minecraft window, but that one was just as slow. The second minecraft window quit properly, but the first one is still open.