you don't need the port forwarding when you're at home, since you're in the same network as the computer, ie. no need to forward anything in through the router from the internet, well, since you're not on the internet, you're connecting from your house...
now, when you're trying to access your computer from the internet, that's when port forwarding comes into effect.
what address are you trying to access when you're away? if it's a 192.-something, or a 10.-something, or a 172.16-something you're still trying to connect as if you're at home, not away..
go to
www.whatismyip.com, that's the address you need to go to when you're not home, ie. connected to the internet.
all the port forwarding does, is send traffic to the router on a certain port, to a specified device (your computer) on your home network, bridging the gap between the real live world and your own network at your home..
make sense?