website showing Blank Page

Hello,
Website was working fine but now its not being just showing blank page http://www.sbmhs.com/.
I wrote email to Hosting company but they are saying problem is in your code and insert PHP Error Reporting code to find out your error.

error log showing Call to undefined function add_action() in /tmp/sess_d912e00fc5d5ebd4befe7d41aec2297a on line 241