500 Internal Server Error

[diamondbuild]

I went to bed last night, my forums were fine 
I woke up just now and I'm getting 500 internal server error on just my forums. Everything else on the site is fine.
I've tried everything I can to fix this but I can't work out how to
Any help would be greatly appreciated
Thanks
Seth

[retrib]

have you recently in stalled new lang packs or modifyed them?

this may be cache problem

[JBlaze]

Internal Server Errors happen when something has gone wrong on the server side. Contact your host if this problem is still persisting.

[diamondbuild]

Nope as I said I went to bed it was fine, I woke up it was broken and I haven't changed a single file 
My host say it's nothing they've done, and they don't know how to fix it

[JBlaze]

My host say it's nothing they've done, and they don't know how to fix it

That's a cue to get a new host. 500 errors don't just happen for no reason, and if they don't know how to fix it, then they are crap.

If you can attach your server's error logs, I can take a look at them for you.

[CapadY]

Did you try to empty the forumcache ?

I think that's the only thing you can do when nothing was changed

[diamondbuild]

I fixed the problem 
It was because the index.php was chmoded to 777
Now about 80% of my users can get on it, but some people are still getting the 500 error 

[xenovanis]

.. but some people are still getting the 500 error 

They'll need to clear their cache