for windows 7/vista:
1. right click on the speaker icon in the taskbar, click "Playback devices
2. Right click on the Playback Devices windows and click on the Playback tab
, Enable the two options "Show Disabled Devices" and "Show Disconnected Devices"
3. select the default device (Speakers + Redirected Headphones
click the Levels
make sure that the blue speaker icon is enabled and not muted.
4. check the Enhancements tab, and temporarily disable all enhancements.
feel free to post here if you still have problems.