4. Video calls don't work
While there are many potential reasons that Hangouts won't initiate a video call, here are a few of the most common troubleshooting tips.
First, the Chrome browser doesn't require a plug-in for Hangouts to work... unless your company uses Google Apps, in which case you will still have to install the Hangouts plug-in to make video calls. It's also a good idea to install the Hangouts Chrome app, which adds Hangouts to the Chrome App Launcher, where you can initiate a new video call.
Note that Hangouts does not support a handful of webcams, microphones, and audio devices. Presuming this is not your issue, make sure the correct audio gear is selected within Hangout's settings menu. To find this menu, initiate a new video, then click the gear icon.Hangouts may work better if you select specific devices for each of the three options instead of "Default."
Finally, in general, restarting your browser and/or your computer is also a good cure-all for any video-related problem within Hangouts.
5. The Hangouts Browser plug-in won't install (or disappears)
Can't install the Hangouts plug-in? First, make sure you aren't running 64-bit Internet Explorer, as the plug-in is not supported on this browser. If you're using Chrome, check chrome://plugins/ to see if the Google Talk plug-in is installed and enabled. (The name is a remnant of Hangouts' prior incarnation.)
You can also try uninstalling this plug-in (instructions can be found here) and reinstalling it. Remember that the Hangouts app is different from the Hangouts plug-in. (You don't need the former, but all browsers except Chrome require the latter.) If the Hangouts app has vanished from Chrome, simply re-enable it by re-downloading it from the Chrome Web Store.
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