When i log in,
there is a black screen and there comes an errormessage with WSAE or somthing like that,
but the Website shows, that 16 Players are Online...
If you suspect that the server is frozen, check the player list, wait five or ten minutes, and if it still exactly the same there is a good chance the server is down
Another way is when you suspect it to be frozen check whose on the forums, because when the server is down some people check the forum. At least thats what I do.