fatal error: call to undefined function wp()

Fatal error: Call to undefined function wp() in /home/web82/public_html/blog/wp-blog-header.php on line 14

you need to be sure you have a file called:

wp-config.php

if you already have it, make sure you have the permissions to 777

or if you dont have one, there is one example:
wp-config-sample.php

change the name of that file to wp-config.php and change the database connection configures

ok, as a last resort, if you dont have one, you can copy and paste this code and create the file with your settings