The mcGateway and the PC that you are using to connect do need to be on the same subnet.
It is hard for us to help troubleshoot as many routers are different and have different settings. I would suggest doing a web search on your particular router and see if you can find a troubleshooting/information website that can help you (maybe there are blocked ports or some other setting that is not allowing communication?)
Again, at the end of the day, once you have the gateway and your PC on the same subnet, you will be able to communicate with the gateway properly
Hope that helps!