Basically you've woken up this morning, visited your website, and all your K2 articles are gone !!!! If you login to your Joomla! administration panel (back-end) and look under k2 items, you should get the following error: Warning: Invalid argument supplied for foreach() in/home/public_html/administrator/components/com_k2/views/items/tmpl/default.php on line 80

As the instructions to installing a new payment module in Virtuemart for Joomla! I've done this video showing how I apply it to my demo site.