Okay few things.
1st, as vb.com would say
To troubleshoot this, first 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. Also be sure to upload the admincp files to whichever directory you have set in your config.php file. Then run 'Suspect File Versions' in Diagnostics to make sure you have all the original files for your version and that none show 'File does not contain expected contents':
Admin CP -> Maintenance -> Diagnostics -> Suspect File Versions
[Note: In some cases you may also need to remove any of the listed .xml files in the includes/xml directory.]
Next, disable all plugins.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php
define('DISABLE_HOOKS', true);
Then if you still have this problem, 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. Do you have the same problem?
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obviously some of the above will not apply to you, but that is the general first thing you do. Check your plugins and hacks you have done to your board!
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2nd, you said your database was compromised a few months ago or something. Well that rings alarm bells straight away.
Provide more info on this aspect and it may shed some light.
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3rd, are you the only admin?
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4th, are you on shared hosting or a dedicated server?
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5th, What vbulletin version are you running?
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6th, what version of php and mysql are you on?
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Once I know the above info, we can go from there.