v139h ipn_main_handler.php missing, reloaded, now paypal doesn't move from the page.

Everything was working fine. I had some problems with a security breach on my hosted site a few weeks ago. I cleaned all of the files, changed passwords, and have monitored the site. I am using a COWOA with quite a few modifications, so I tried to avoid an upgrade.
I was notified that paypal gave a 404 error. I realized that ipn_main_handler.php did not exist. (My virus software reallllly cleaned everything.)
I found a previous copy of my site/zen-cart folder and ftp'd it in.
Credit card orders have worked fine. When a customer clicks the radio button on paypal, and clicks 'confirm the order', it attempts to give them a 'success page' (the same success page that a successful credit cart purchaser would get, but the paypal customer never saw a payment page), but than comes back to index.php?main_page=checkout&fecaction=null. It never heads to paypal.
Attachment 12687 I talked to paypal, and they can't help.