Volume Mixer in Windows 7, not just show device volume but also lists all applications that are currently running and producing the audio. You can control the audio of any of the application from there on. So when you are having more than one application that is producing sound you can control from here and stop it as well.
In windows you can search for keyboard from start menu and open keyboard settings. Or you can go to Settings > Accessibility > Keyboard. In the keyboard settings window, toggle the switch that says "Use the Print screen button to open screen snipping". Hereafter whenever you press print screen button, you will be able to make a selection on the screen for a screenshot.