In Windows 7 and 8 a featured call User Account Controls (UAC) will prevent WavPlayer from changing the Windows default settings. You will have to turn the UAC off.
Disable UAC on Windows 7 and 8
Windows 7 makes it much easier to deal with UAC settings. Just type UAC into the start menu or Control Panel search box.
You can simply drag the slider up or down, depending on how often you want to be alerted.
If you drag it all the way down to the bottom, you’ll have disabled it entirely.