Fatal Error

My site seems to be down, when i run the site url through SucuriSiteCheck it get this error:
Site error detected.

Details: https://sucuri.net/malware/php-error-fatal-error
<b>Fatal error</b>: Call to undefined function wp() in <b>/home/a1207396/public_html/wp-blog-header.php</b> on line <b>14</b>

I’m a bit of a newbie. What does this error mean and how do i fix it? Here is the site link: https://hitechdigitallifestyle.net63.net. Any help would be greatly appreciated!