I am certain I installed and updated PB correctly. Googling it finds lots of folks having problems running COD4 in Win 8.1 but I did come across something that jogged my memory of trying to get it working when Win7 came out, involving stereo mix. I'll try this on my lunch hour:
"If you are playing Call of Duty 4 on Windows 8, and you encountered following error : iw3mp.exe has stopped working , this is how you can fix it. First, go to Control Panel, Sound, and then click on recording tab. When in recording tab, right click and mark "show disabled devices". There you should see "stereo mix" , just enable it and go play Call of Duty 4 : Modern Warfare. The fix in this post works 100%, but not all systems are the same. Another trick is to plug in your headphones in the headphone jack. After that you can unplug them when the game starts."