Juniper Firewall setup

Question

I bought an old Juniper 5GT firewall simply to do some port filtering. I have set the device up in a DMZ zone of my home network, there is a server behind it and it has been assigned an IP by the firewall. The router of my home network has assigned an IP to the firewall but not anything behind it.

Here is a basic map of my network:

http://puu.sh/7Yqjc.png

Currently I can not reach the server from outside the firewall (Untrusted), however the server has access to the internet. I need it so I can access the server that is behind the firewall (through ports 80, 22 and 21 the rest should be blocked by the firewall). What have I missed, or is this not possible? I dont see much use in a firewall if this is not possible.