I can't log into the game, everytime I try I get a black screen.

Are you trying to play from school? The game (and other flash games) are blocked at some classrooms in my school so I can't access Wartune there. Your problem might be similar, and there is no way around it because the rule is enforced on the router where your connection goes through.

If you're at home, check your firewall/router settings and/or update flash player.

One more that isn't suggested there. Also you can clear the cache from the current browser and/or attempt to use a different browser all together. I've heard multiple stories where the game would just start randomly working for people again as well.