Hello. I bought this game yesterday and I can't really play it...

CPU: i7 860 @ 2.8 GHz
GPU: GeForce GTX 580
RAM: 8 GB
OS: Windows 7 (64 bit)

My drivers are up to date.
I've tried reinstalling.

Singleplayer:
I can play singleplayer for a little while, then it crashes.
It crashed two times in a row in the same place, on the first map, when you've infiltrated the base and enter a little house and do a stealth kill, while another guy walks into a "orange tube". When I get 1 meter into that tube, the game crashes.

It has also crashed after the first intro and also after 1 minute or so when you get ammo to your first gun.

Multiplayer:
Router/Modem: Thomson TG789vn

It says I have NAT Type: Strict.
I've searched for the problem on google and people says something about opening ports.
I have no clue what so ever how to do this. Can someone tell me a step by step guide how to fix this?