I have been to many forum sites and tried many solutions already , I have downloaded the latest patch and tried going to the control panel>sounds>recording( I don't have the stereo mix) I'm using windows 7
but still it says "iw3mp has stop working" and here are the details

Problem Event Name: APPCRASH
Application Name: iw3mp.exe
Application Version: 0.0.0.0
Application Timestamp: 4859a219
Fault Module Name: iw3mp.exe
Fault Module Version: 0.0.0.0
Fault Module Timestamp: 4859a219
Exception Code: c0000005
Exception Offset: 0027782e
OS Version: 6.1.7600.2.0.0.256.1
Locale ID: 1033
Additional Information 1: 0a9e
Additional Information 2: 0a9e372d3b4ad19135b953a78882e789
Additional Information 3: 0a9e
Additional Information 4: 0a9e372d3b4ad19135b953a78882e789

Please Help :(

That happened to me also, I reinstalled the game and it worked fine for me. Just takes about 10-20 mins to install. Hope this helps.