Now, I actually already made a hotkey to mute the volume.
I got nircmd and put in this command,
Nircmd.exe mutesysvolume 2. The problem is that it doesn't work when I start up a PC game (like battlefield or grand theft auto).
Now, it used to work when I had Windows XP 32 bit. I now have Windows 7 64 bit.
Is there a way to make it mute the volume when I have a game running? (on Windows 7 64 bit)