I've tried this recommended by another member.
To troubleshoot this, remove any hacks and disable your plugins, then see if you still have this problem.
If so, reupload all the original vB non-image files (except install.php). Make sure you upload these in ASCII format and overwrite the ones on the server.
Next, create a new style and choose no parent style. This will force it to use the default templates. Finally empty your browser cache, close all browser windows then try again. Make sure you change to the new style and view your forums with it.