PHP script fix preventing site from loading properly

I have had my site recently moved to a new host. I've also had customed PHP work done. Some previous customized PHP login scrip is loading up improperly when the URL is browsed, preventing the site from loading in most browsers. I need this removed quickly so that my site can be viewed properly. I need to ensure that any scrips previously installed which were sending information to another site through an API have been removed completely so that sensitive information isn't improperly transmitted. Results of a cross browser platform test, such as available at [login to view URL] will be required to prove that site is working with most widely used versions of major browsers (Firefox, Chrome, MSIE and Safari) for PC and Mac.)