Hello,
My name is Matthew. I have several years experience in PHP and Zen Cart and run my own store. I am happy to help you fix the errors in your store. It looks to me like the problems you are facing aren't as such a database problem. More likely with these errors, your host has upgraded your version of PHP and some code is now incompatible. If you are interested i can patch these errors, and fix any other problems that may be preventing your site from opening.
Many thanks,
Matt de Marillac