14120 PHP and MySQL Slowness issue

I need an PHP and MySQL expert to help with the slowness of my website. Have a listing script loaded on our site with thousands of records in a MySQL database and it is taking 100+ seconds to load a page on avg. Our hosting company has already moved us to a different server to see if that would solve the issue, but no resolve. We have a different domain on the same server running the same script and it is not taking as long to load, so we just need someone who can troubleshoot why/where the slowness is coming from and correct and/or suggest actions to correct. Also need help in implemting a better sign-up process for users who will sign-up on our site.