medx.info has bombed out!

All of a sudden I get this when trying to browse www.medx.info!

Fatal error: Call to undefined function node_load() in /home/.hilarius/medx/medx.info/includes/menu.inc on line 408

I have tried restoring from backup - FTP's all the backedup files from local pc the site.
Then I deleted everything and copied afresh original Drupal 6.3 files - still the same error?
That is strange - it is supposed to treat thi slike a new install.

I need help URGENTLY!

Thx!