Right-click the speaker icon in the Windows Taskbar.
Select "Playback devices"
double-click on the device and you should or might see an enhancements tab...with options like Bass Boost, room correction, Loudness Equalization, etc. depending on your actual sound card. Usually enabling the Bass Boost, and the Loudness Equalization will fix the low-sound problem in Vista, Windows 7, and Windows 8.