OK here what I did.
1) Download .htaccess to PC and delete the one on server.
2) Add this code at the end of .htaccess file.
PHP Code:
# All other pages
# Don't rewrite real files or directories
RewriteCond %{REQUEST_FILENAME} !-f [NC]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*).html$ index\.php?main_page=$1&%{QUERY_STRING} [L]
3) Upload .htaccess file back to home directory server (using Binary not ASCII).
4) Change .htaccess file attribute to 666 and refresh the page (which is /best_sellers.html).
5) Page appears correctly and change .htaccess file attribute back to 644.
6) Done
Thank you!