There can be several things going on.
First, it sounds like you are may be talking about accessing your public IP from within your private network, attached to the private IP side of your server. That requires two things to be working: your server software needs to be attached to the public IP, and your private IP needs to forward to your public IP (and back).
So, the first thing to do is figure out which of those is not working. Go to another Internet access point, outside your local network, and try accessing your public IP. That will tell you if your server software is attaching to your public IP address, and that your firewall is allowing outside connections through that IP.
If that works, try connecting to some other publicly-accessible port on your server from inside your local network. If that fails, there can be a range of issues, from your firewall blocking access, to NAT not passing packets one way or the other.
Following those instructions, you should at least get closer to your solution. If you post your findings, along with some more details about your configuration, and we can help further.
On the other hand, if not being the server administrator means that you don't have access to the logs or firewall configuration, you will need to speak with the person who does.
