There are a number of causes and possible fixes for this issue
1) I'm assuming you are running a legitimate copy of Windows 7 (The Cracked RC Versions are known to cause CTD issues)
2) You have the latest dirvers for your GFX Card (Steam / Windows 7wrongly detecting older version ATI or Nvidia Drivers may cause CTD)
3) You have set and forced your DX to the version you are using (9 / 10)
What you can try, failing or passing all of these is the following:
Disabling your Onboard Sound and testing for stability (Realtek Related Issue)
Unplugging or disconnecting any USB Mic you may be using and Testing (USB Mic Audio Driver Issue)
Updating onboard Sound Card Drivers
Enabling Stereo Mixing On Realtek Sound Cards