how do you know that? does it give an error message? if so, what is that error message? if it does not give you any error messages how do you know it is a problem with the database?
we need details or we can't possibly know what to tell you to fix whatever the problem is that you are having.
Edit: if you are talking about this board: http://www.robuild.co.uk/forums/
I see the database error :
Unknown column 't.topic_visibility'
that usually means that you have upgraded a 3.0 board to a 3.1 board but did not run the install/database_update.php file to its completion.
however, since there are no posts showing on your board at all but in the stats it says you have a lot of posts, I would assume that you did not update the old database properly to begin with.
please explain exactly what you did to get to this point.