Some people seem to be having issues. Try incognito mode to see if your cookies are affecting it.
Not sure what you can do if cookies are not to blame.
I can get to the main page, but I can't actually load into any battle. It'll say 'now connecting...' for a bit, but then that disappears and it stays as a completely black window.
And I'm getting this on two different computers.
I thought I messed something up by playing on ipad as well. That or because I have just updated Java.
Guess I'm not the only one.
Strangely, I can still play on ipad :| ...
Clearing cache might help. If not, clear cookies.
It's strange how those things can sometimes affect Nutaku, but it's just Nutaku things.