If you are currently running Vista or Windows 7, please complete the instructions in the following link:
If you are running in Windows XP, take the following steps:
1) Exit Steam.
2) Go to the "Start" menu, select "Run", type "regedit" and click "OK".
3) Navigate to the following registry key: HKEY_CURRENT_USER\SOFTWARE\VALVE
4) Right click and select "Permissions"
5) Check the "Allow" boxes for "Admin" and "System" for both "Full control" and "Read".
===========================================The remaining steps apply to *all* versions of Windows.
Please verify the GCF for this game as outlined here:Note: Files may fail to verify. This is normal and can be ignored.
Then test the issue.
If you still have difficulty, you may also need to manually run secondary installers required by this game.
Exit Steam entirely.
Browse to your Call of Duty: Modern Warfare 3 installation folder (Usually C:\Program files\Steam\Steamapps\common\call of duty modern warfare 3\)
Run the following installers:
...\Steamapps\common\call of duty modern warfare 3\redist\directx\dxsetup.exe
...\Steamapps\common\call of duty modern warfare 3\vcredist_x86.exe
Reboot your computer and test the issue again.
If the issues persist, please complete these guides:
Further support for this title is handled by a third party support department - please follow the instructions below to contact the support provider to troubleshoot this issue: