Listen to me..i might have the solution..
I had about 80% of my games where the NAT issue was there.
What i did was, go into:
Type this into your web browser
http://192.168.0.1/A log in box shoud appear and type in the USER NAME - ADMIN and then type in the PASSWORD your isp name, mine is SKY (for sky broadband).
It should log you into the router.
At the side there are some tabs, go to WAN SETUP and where it says DEFAULT DMZ SERVER next to that should be a ip. Now, look at the last box with a single digit number in it, this should be matching you computers IP.
Now minimise your internet window.
Go to RUN>cmd>ipconfig
Look for your ip and look at its last number...for example, mine is 192.168.0.5
Look at your routers ip and if the last numbers dont match change your routers last number to match your pcs ip.
If you have done all that press APPLY.
Restart your router and it SHOULD have worked, if it hasnt add me on xfire and we will talk.