Have just completed my new build 2 weeks ago and all was well.
I then lost the sound completeley, went to the gigabyte website, dowloaded and installed the latest realtek drivers for Windows 7 64bit, and sound back again.
Yesterday the sound went again, so went back to the site and downloaded, unistalled, rebooted, installed, rebooted, blah blah and still no sound.
I am using the onboard sound via a single jack on the rear of the pc to 2 speakers, not any fancy HDMI or spdif. All the settings are correct and according to the sound level monitor in Windows 7, sound is playing!!
The speakers work fine on my other PC (Running Open Suse)
Gigabyte UD5 board
6gb DDR3 Gskill memory
2 x 1tb WD cavier blacks in raid 0
Windows 7 64bit
Any help appreciated.