Go to Google

Search for DirectX

Download the DirectX Web Installer from Microsoft

Run it

Reboot your pc

Try the game again

That should work however if it doesn't then you need to put the disc in the pc if you have the disc.

Open My Computer

Right Click on the Disc

Click Explore

Open DirectX folder

Scroll Down to Setup.EXE

Run It

Reboot

Try the game again.

If that still doesn't work then try this

Open Steam

Click Library Tab

Right Click on Modern Warfare 3 Multiplayer

Click Properties

Click the Local Files Tab

Click Verify Integrity Of Game Cache

Let it run

Do that for the Single Player as well

Reboot

Try the game again

If that still does not work

Check if your Motherboard, Sound and Graphic's drivers are up to date and if they are not then update them, then try the game again.

If that still does not work then try a fresh install of the game and see if that works.

If that still does not work then try this if you have a 2nd hard drive.

Move data from the 2nd Drive if possible to the C: Drive

Turn PC Off

Remove Sata/IDE cable from the C: Drive

Install Window's on to that drive

Install all the updates and drivers

Install the game and try it.

If it works then you can simply install everything else but I would suggest after installing each program/game etc that you try the game so, that you can see if one of the games/programs is causing the issue.

If that does not fix it then you could see if the Bios is up to date as that has helped some people as well.

Hope something from this help's