I ran into a bug where sometimes Windows Media Center would auto-mute sound upon resume. To fix this, I used eventghost.
1. Download and install Eventghost (or list of downloads here)
2. Open up Eventghost
3. Create Macro. Name it Turn Mute Off
4. Create new event (System.Resume). In order to find this I hit sleep on windows media center remote and hit it again to wake computer up. On the left side of eventghost window you will see the most recent activities recorded. Drag the System.Resume event over to the night under the macro you created.
5. Create action. Double click on system, then double click Sound Card, then select Turn Mute Off.
6. Save it
7. Test it out by first muting windows (not receiver mute but actual windows mute). Then double click the macro and it should turn the mute off.
Should look like example below