WP Memory size exhausted

Hi I recently change the theme of my wordpress based site and install all plugins. I am now unable to access my dashboard as I assume there are too many plugins installed. I have asked my host server, Hostgator, to look into this issue and increase the memory but they ran into a problem of saying my database does not exist. Our website was initially set up my a web designer whom we had a falling out with, we thought we had all issues resolved when we switched ownership back to us and created a new database. Would you please help me look into this problem? Thank you!