All Links currently broken

So my forum was working perfectly fine this weekend when all of a sudden it stopped working.
The site is at http://ovcball.net/vanilla.
It brings up my homepage just fine, but when you click on any link, I get a 404 error. There were zero changes made to my site between the last time it worked, and when it didn't.
It's stored on the same host that's running a wordpress site, but that hasn't caused any problems. (Up until now, obviously).
Any ideas as to what could have caused it? Or how to fix it without starting from scratch?
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Comments
you can see it is working (just not pretty urls)
http://ovcball.net/vanilla/index.php?p=discussion/153/pick-em-round-3-jan-26th-games
see
http://vanillaforums.org/discussion/22618/wordpress-plugin-not-linking-to-correct-urls#latest
You probably already have it set to TRUE, but you have lost/overruled the server rules that route pretty urls. That means you server rules have been skewed, typically .htaccess on apace servers.
Note there can be a knock on effect with multiple .htaccess, that is why server purist don't particularly like this solution, but that is the reality for many people.
grep is your friend.