If you reinstall DA (./directadmin i) on a live box, your /etc/httpd/conf/httpd.conf file will get overwritten and emptied of all data. Â You'll need to readd all of the Include lines for your users so that their sites show up (you'll be seeing the apache pages, or the shared IP pages instead)
Type:
cd /usr/local/directadmin/data/users
for i in `ls`; do { echo "Include /usr/local/directadmin/data/users/$i/httpd.conf" >> /etc/httpd/conf/httpd.conf; }; done;