Moodle Login Error - Help ASAP

Hello there Akshay this side,

I had developed a moodle website for my client ( http://student.neweraprofs.com/ ) and it was working fine until I tried to integrate an SIS system to moodle and done some changes in "External Database" settings under plugins and now I can't log in to my moodle website.

It is giving the following error :

Exception - Call to undefined function mysql_connect()More information about this error

The screenShot is also attached ( https://prnt.sc/ur0rjb ). Please help me ASAP as students are trying to login but no credentials are working now including the ADMIN's login credentials.

Thanks