The problem with videos not loading in Google Earth balloons has to do with the flash player plugin for the Google products. The long and short of it is that Internet Explorer uses a different type of plugin (activeX) than Google Chrome and Google Earth. So when you update the flash plugin in Internet Explorer, it doesn't update the one needed for the Google products.
To fix the problem, you can click on the link below and it will take you to the manual download for the correct plugin and it will guide you through the install process.
The file should install quickly and after it is installed, start Google Earth and your videos should now play inside the balloon.