I came across a forum post where someone asked how to programmatically mute the Windows System volume. So this is what I have found:
NirCmd
NirCmd from NirSoft is a small command-line utility that contains many smart functions like muting and unmuting the system volume.
To mute the system volume, simply run the following command
nircmd.exe mutesysvolume 1
and to unmute you run
nircmd.exe mutesysvolume 0
With VBScript
Another option is to use a VBscript, the following code I found here will mute or unmute the system volume
Set WshShell = CreateObject("WScript.Shell")
WshShell.SendKeys(chr(&hAD))
SndVolPlus
Although it doesn’t allow to automate muting the volume, SndVolPlus is a nice replacement utility for the default volume control in Windows. SndVolPlus can do everything the standard volume control does, but also allows you to mute / unmute the volume by just double clicking on the volume icon. SndVolPlus can be downloaded from here