Problem with web-sharing and resolving localhost
Judging from your feedback in the comments, the installation of PostgreSQL brought its own version of libpq (which then got removed during un-install). To fix

cd /usr/lib
sudo rm libpq.5.dylib
sudo ln -s libpq.5.3.dylib libpq.5.dylib


Then run apachectl configtest again to check for further errors.