PHP WPAU Admin

Our webhost is upgrading to PHP5 and indicated an upgrade to the latest WordPress was required. I used the WordPress Automatic Upgrade plug in and first, all the pictures and pages were lost. Then in an attempt to restore, got the FTP back what I had saved, then went into phpMyadmin and to replace the previously saved database backup. Now the entire site has disappeared. Can’t log in, nothing but a blank screen appears. Where is the problem likely to be and what is the best way to solve it? Thanks for any advice.