May be your firewall or antivirus blocking your game, and have you updated your BIOS and have the latest dirvers for your video card.

Turn off anti-virus and firewall to see if you can get past the load screen...

Have you looked in event viewer to see if anything shows up that can help,

I have the same problem, my games freeze at main menu after few seconds..i have nvidia gtx 675m with latest drivers. Before installed beta driver released for black ops 2, my games worked fine. (sry for my english)

Beside the good hints above to update drivers, verify game cache via steam and to check the reasons for the game crashes with the window owned Tool  >eventvwr.exe<  like Hootymadman already said I would suggest to:

- open your MW3 Ports --> check internet:  MW3 +open ports +name of your router

in Order to get NAT-Type: open

- keep in mind: the MW3 game engine tries to balance the matches by adding lag to people with high-performance computers and connections - which means: if you have high FPS and GPU usage and low ping or host, the game will see this as an advantage and add latency to your client. This means that the more GPU usage you have - the more time advantage your enemies will have over you!

http://forums.steampowered.com/forums/showthread.php?t=2253196

Good luck ;>