Solution:
Its permalinks problem,
First make sure that your sub pages are working with default permalinks
go to settings->permalinks
choose “default” and save and try to navigate, if this is working fine then
replace the .htaccess code with this
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
and revert back the permalink structure to which ever structure you want,
Best thing is choose “Postname” in permalinks