So you have some Links and or buttons that do not work correctly. This is common problem and the primary solution is to switch your SEF URL’s off. Then make sure you have the right URL set under Admin-> Configuration-> Site(TAB)-> Site URL and Secure URL. You should also make sure that your configuration file also has the right URL. You’ll find it under JOOMLAROOT /administrator/components/com_virtuemart/virtuemart.cfg.php. Don’t forget the trailing slash. Also make sure you have a menu item linking to VM component and the mod_virtuemart module published.

VirtueMart does not work very well at all with Joomla SEF URL’s.  If you think that this doesn’t apply to your install, then you should reconsider; this is the first thing to do when you have some sort of linking issue. Actually they say you should never have enabled it until you are done with your site. If you want SEF URL’s, its recommended get one of the third party extensions for SEO links.

If your add to cart is not working. Then switch off your AJAX add to cart. This function is known to have major issues with other javascripts, like the ones that may be implemented in your template or in other various modules or extensions.  LOCATION: Joomla backend-> Components-> Virtuemart-> Configuration(under Admin TAB)-> Site(TAB)-> Layout(section)-> Configuration