Need help port forwarding using imac

Setting up a new router and want to open port 12000 however when I assign a static ip to my imac when port forwarding, my imac although connected to the router will not connect to the internet. Router is DGN1000. Any ideas guys, i tried the www but no luck.

Thanks for your reply Sandman. I was putting a static ip in using the manual option which gave me problems. When i put in a static ip using the
dhcp & manual option hey presto. I'm getting too old for this shit man lol.