Hello,
I was having serious issues getting source to launch. I applied all the fixes listed in the links below and was still getting the same problem.
http://forum.bitdefender.com/index.php?sho...=counter+strike
http://forum.bitdefender.com/index.php?sho...on't+launch
Add a rule in antivirus exclusions...
From expert view.
      - Click antivirus tab
      - Click Advanced Settings Button
      - Click Exclusions Tab
      - Click the small + button
      - locate and select C:\Program Files (x86)\Steam\steamapps\%steam user%\counter-strike source\hl2.exe
      - After that is added to your exclusions click ok
      - Close bitdefender and launch counter-strike source
I hope this helps. Please let me know if this worked for you.
Have a nice day