Was this grahics card bought brand new, i asked this before ? Possible to it could be faulty or damaged. Strange problem that you have to disable the HDMI Audio device to download new driver, should have nothing to do with downloading something or anything.
HDMI Audio Device is listed because for one, HDMI also carries audio and this must be way you are hooked to your monitor, but must be using the onboard graphics cards HDMI port on PC at time, not one on the ASUS Radeon card.
As said before, looking at Gigabytes site i find no drivers for this board, except USB 3.0 which is odd. Did you receive a disk with this system with system drivers for this board when purchased ? Another symptom of this issue can be outdated drivers for systems board, e.g....( controllers, chipset) Last BIOS for this board was 2012. Could also try contacting Gigabyte, will not charge you. pretty good at helping, as i had called them twice as mine is also a Gigabyte board.
Another is to test the Hard Drive, even though did a fresh install of Windows 8.1, at Command Prompt (Admin) copy and paste
chkdsk /f
Let this run, will take sometime, then can get a text document on desktop and post here from chkdsk results by doing this :
1. Press the Windows + R keys to open the Run dialog, type powershell.exe, and press Enter.
2. In PowerShell, copy and paste the command below, and press Enter.
get-winevent -FilterHashTable @{logname="Application"; id="1001"}| ?{$_.providername –match "wininit"} | fl timecreated, message | out-file Desktop\CHKDSKResults.txt
3. You will now have a CHKDSKResults.txt file created on your desktop that is the log file of your chkdsk scan results from Event Viewer.
Check RAM could be another issue, this takes time windows 8.1to do,find the Memory Diagnostics tool, in control panel under Administration Tools.
Incorrectly configured, old, or corrupted AMD HD Audio Driver device drivers. (very common) Shown in link i gave you earlier.
Your board has a AMD integrated graphics, then feeling possible driver conflict or hardware conflicts here.
Hardware conflict after installing new Advanced Micro Devices, Inc. hardware, or hardware related to atihdwb6.sys.
Trying to think of way around this if this new card is truly not faulty in anyway. When card is installed can go to Device Manager and uninstall the integrated graphics drivers. Problem i do not like about this is process of getting these drivers back if needed for integrated card, if this is the conflict.
Usually done in Device Manager by going to the top menu, select View and Show Hidden Devices. Then go to Display Adapters open it and shaded one would be other integrated card, this would be only when other ASUS Radeon cards driver is properly installed would not be shaded. Whichever is default card at the time.