Changing your DNS server wouldn't affect your ability to forward ports.
I tried opendns in the past, but quickly stopped after I found they hijack non-existent domains and fill them with ads.
Some good, free ones you can use are 4.2.2.1, 4.2.2.2, 4.2.2.3, 4.2.2.4, and 4.2.2.5.
Ping each of them, and use the two with the lowest ping times.
As for your port problem on the router, can you just not access your router anymore? Or do ports just not forward correctly? Little more info would help.