Hey, to start the game and pause the game you need to press H. Hope it didn't cause that much confusion.
H does nothing (windows 32bits and 64bits). It stays on a gray screen. What should I do?
That's really weird, you should see the help screen and h should start the game. If you are not seeing the help screen it means some stuff didn't load.
My suggestion would be:
1. Download the game again.
2. Update Java.
If that doesn't work I have no idea. Sorry :/