If there's no sound through your monitor and there's also no High definition Audio in the "playback" tab in sound control panel, try this:
1. start>right click on "computer" click "properties">Device Manager
2 Go to sound, there should be one called AMD High definition audio or something i forgot the name>right click Uninstall>when a confirmation window appear tick the "Delete driver software for this device".
3 after it finish uninstall, click the scan for hardware changes at the top of the device manager.>the name should be change from Amd High definition audio to High definition audio.
After this procedure, the high definition audio should appear on the sound control panel, set it as default this sould fix your problem.
Gigabyte GA-Z77X-D3H, Intel i5 3570k, 2x4 GB Kingston, Sapphire HD 7950 Vapor-X, Seasonic M12II 850W, Windows 7 Ultimate x64, Seagate 500GB, Seagate 2TB