White screen of death

Guys,

Need help urgently as my site has been offline a couple of days now. I’m getting a white screen of death… here’s what I’ve tried:

plugins have all been disabled by ftp
switched to default theme
refreshed all wp core files via ftp except wp-config and wp-content

When I try to access wp-admin I get the message:

Fatal error: Call to undefined function nocache_headers() in /home/makewood/public_html/wp-admin/admin.php on line 33

However, I’ve repeatedly refreshed the /wp-admin/admin.php file with freshely downloaded one and have searched it for nocache_headers()….. can find any sign of this line.

Here’s the url: https://makewoodenlures.com

I really need to recover this site urgently. Any suggestions appreciated.