That's very strange (and worrisome) would you mind posting a screenshot? The game seems to function fine on my end, what version of Windows are you running it on? I'd like to fix this but without the error occurring on my end, and without knowing what you're running it on it's gonna be tough to fix :(
unfortunately I'm at work and thus can't really test anything, however I did a few quick Google searches and while I didn't find anything about half the screen going black, Rpg Maker games not working on Win 8 isn't ENTIRELY uncommon, so maybe you can search some solutions :/
EDIT: Found this on the Rpg maker forums "This person was having this exact same issue, @Andar said "Most likely a problem with either the browser or your display driver. Please updatew your display driver (MV uses OGL, not DX - so an older OGL library in your display driver can be a problem even if DX-Games work without problems) and test if the same happens if you start the project's index.html directly with Firefox or so." on that post.
But looking back on the post itdoesn't seem it's been resolved.
https://forums.rpgmakerweb.com/inde...-screen-while-game-testing.81741/#post-759508"