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. 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;
Note that this add the include lines for *all* users.. so if you've added users to DA after you ran the ”./directadmin i”, you'll end up with duplicates. Make sure you dont have duplicate Include lines.. (apache won't restart, it will let you know)