Pretty much the standard 3 things you check.
First be sure you are using the correct public IP. Also verify that the IP you see on the wan interface as your router is the same as you see on a site like whatsmyip. If these are different you do not have a public IP.
Check the server actually has a process open on the port. You should be able to see it in the resource monitor network tab. You also if you can connect to the server from the lan using the local lan IP.
Many times the port forwarding rules are strange try DMZ instead since it is easier to get setup.
After that you need to determine how far the traffic is getting. I would start by loading wireshark on the server and see if you see anything when you scan the ports.