Here are two links with lists of suggestions to try to help fix the freezing/crashing problems people are seeing in Modern Warfare 2. Taken from the link below:
http://www.unigamesity.com/how-to-fix-modern-warfare-2-problemsfreezings/
http://www.gamingnewslink.com/2009/...-errors-freezes-crashes-and-install-problems/
Your most likely fixes include:
* Try updating the video and sound drivers (looks like sound drivers have caused this issue for others) on your computer. Also, try lowering the resolution levels and load the game once more.
* If this still doesn’t solve your problem and Modern Warfare 2 keeps freezing, and you are running Windows 7, right click the game executable and select its properties, then set it to run in compatibility mode with previous versions of Windows (Vista, 32 bit or XP).
* Finally, another possible Modern Warfare 2 fix is suggested for those who have Windows Vista. Jlesamiz suggests trying the same tweak that worked with the original Modern Warfare:
“Click Start > Run (or Windows Key + R), type in this command followed by Enter:
mmsys.cpl
Click on the Recording tab.
Right click on *any* entry in this list, make sure “Show Disabled Devices” is checked.
If you have an entry for Stereo Mix, right click on it and choose ‘Enable’.
Then, restart your computer and retry running the game.”
* Some people just suggest waiting for a couple min and that cleared the issue. They suspect that this will be fixed in the next patch release.