I have been using my homebuilt PC for about a month now. A couple of day ago I detached the video card (Sapphire Radeon HD 7950 OC Vapor-X) to RMA it (extreme coil whine). My MoBo is an ASRock Z77 Extreme4 Pro.
Since removing my video card I have had no sound. After trying all of the normal things I stumbled across an interactive map of my MoBo in the BIOS. Normally if there is nothing plugged into the socket there it will tell me that is it 'empty'. The 5 3.5mm jacks at the back now inform me that they are 'disconnected'. I have reinstalled the latest audio drivers as well as removing the old video card via device manager. I am now using the integrated MoBo graphics.