If you're like me, you fumble around trying to pause your PC's media player every time the phone rings. The easiest way around this is to buy a multimedia-capable keyboard that has a mute or Play/Pause button. If you don't want to spend the money or you already have a keyboard you like, I have a workaround using NirCmd that allows you to mute the system volume from the keyboard.
If you don't already have a utilities directory that's in your system path, follow my instructions to create one. Next, downloadNir Sofer's excellent, multipurpose NirCmd utility and extract it to your utilities directory.
The NirCmd page has a complete list of commands for the application. The command we're looking for mutes and unmutes the system volume:
nircmd.exe mutesysvolume 2
To run this command with the keyboard, we'll create shortcut on the Windows desktop and then assign it a key combination. Right click an empty area of the Windows desktop and click New->Shortcut. Fill in the command line noted above and then click Next.
Name your shortcut and then click Finish.
To assign a key combination, right-click the shortcut and then click Properties. Click the Shortcut key box and press the keys you'd like to mute the system volume. I chose CTRL+ALT+, which takes precedence over any application-specific shortcuts. If you use CTRL+ALT+V in your other applications, choose a different key combination.
That's it! Now you can mute and unmute your PC by pressing CTRL+ALT+V.