Reconfigure Plesk to use your vhost file
I never remember how to do this even though I often find myself fiddling with vhost files
This works on the Dedicated Virtual Server (3.5) that I use most often from Media Temple, so it may not work in your situation.
Reconfigure your server to use the new vhost.conf file using Plesk's websrvmng command:
/usr/local/psa/admin/sbin/websrvmng -a -v
To carry out the same function on a dv 4.0 set-up you can use
/usr/local/psa/admin/sbin/httpdmng --reconfigure-all