Index displays “not found” when not logged in!

Hi,

my blog crashed yesterday, it just kept on loading for hours. Today it’s back on, unfortunately the start page (index) shows only my customized “not found” message.
Other people have access to the admin area, but the index.php looks fine to me (which it must since it works perfectly fine when i’m logged in…)
I tried turning off all the plugins, which didn’t help.

Have I been hacked, is the WP Super-Cache ??

I would greatly appreciate any help,

Max