From what I saw, it looked like the forum was hit pretty hard by a bunch of spam bots. It's likely the bots were posting too many messages too quickly for the host to handle, thus the site crashed.
Plus, based on seeing little errors like this "Notice: Undefined index: l8fd0 in ...\vb\library\node.php on line 1 " scattered around the site, I'm also guessing that the forum's base files may have been slightly corrupted.
Either way, glad to see the forum is back though!