Troubleshooting Port Forwarding Issues

Hello everyone, I was hoping I could find some help on a rather annoying issue I've been having while attempting to open some ports on my Linksys WRT5GS2 Router.

What started as an simple port forwarding adjustment on my router has turned into something far more confusing. After setting up my Windows 7 PC to connect with a static IP (192.168.1.100) I tested forwarding the port 43995 via my router page for that IP. Unfortunately after testing it with a portchecker tool it still appeared as closed.

My router is directly connected to a wall Ethernet jack in my apartment, and the ISP is a reseller of Suddenlink internet, Korcett (via rateshaper.com). In order to access the internet I have to log first log in to Korcett and register the MAC address for my device, e.g. PC and router.

I immediately presumed the ISP was responsible for the closed ports, and made a call requesting information as to how they could be opened. They told me they didn't close any ports themselves, and said they would assign my router a public IP address, and that I should restart my router.  

After restarting my router I was unable to connect to the internet at all, both via the router and directly connected to the wall. In order to reconnect to the internet I had to manually enter the Korcett management page from a different internet source and delete the registered MAC addresses in order to reregister them. In other words, I'm back where I started.

This is the first time I've had to deal with a router / ISP combination like this (I was accustomed to a much simpler 2wire At&t combination) and this has pretty much exhausted my networking knowledge. What exactly does a public IP do when assigned? What changes would I need to make to connect to the internet using a public IP? Is there anything I should know specifically in order to forward these ports with my unique situation?

Thank you very much in advance for any help or suggestions you may have and please feel free to ask for any extra information you may need to troubleshoot this problem.