Oh that's really weird, what browser are you using? Does the button atleast highlight when you hover over it
Firefox seems to struggle with loading some of the assets since this is a 3D game, I've added a downloadable Windows build but you can also try running the game off a Chrome based browser.
Honestly we couldn't spend much time optimizing for WebGL because of the deadline, but I can look into fixing this for future builds. Thanks for the heads up!