1.) Always use the the default vBulletin style when isolating a problem like this.
2.) Disable all mods/plugins and testing on the default vbulletin skins. If that works re-test on your new skin, the mods/plugins should still be disabled. Once you have done this report back with the results.
To temporarily disable the plugin system, edit includes/config.php and add this line right under <?php
Code:
define('DISABLE_HOOKS', true);[/color]
You can also shut off the plugins from the admincp:
ACP --> settings --> options --> Enable Plugin/Hook System: NO
If the problem disappears then most likely have accidentally modified a template incorrectly or one of your mods/plugins has altered it. This could be due to a modification not being a matching vbulletin version.