Has my site been hacked or the server's error?

[vanpelt]

My forum has gone totally skewiff. It's showing up differently each time you load, usually not the entire page - sometimes just the background graphic, sometimes just the background colour, sometimes the header, and sometimes just script on the page. It is random. When I click on 'members' when I finally get the top part of the forum, I get the entire index page and then underneath the member list starts - like I said, entirely skewiff. Has the site been hacked, and if so what do I do to start fixing it?

Ah, if you look at the page source, you see a heap of links to viagra and other spam. Where on earth has this got in, and where do I look to fix it?

I think it runs 3.6.8.

http://planet-flipside.com/vboard/index.php