Have you checked your OEM's web site for any Windows 8.1 driver for the Atheros Network Adapter, that's if you have that Network Adapter in the first place?
This is only posted as a last resort option.
Most new machines come with a recovery partition allowing you to go back to the time of purchase, you will have to check your user guides (or the manufacturer's Web Site) for instructions. Choosing that path requires you to save all valuable data first. Unfortunately upgrading to Windows 8.1 may lose such Recovery Partition.
These options are built-in to Windows 8 also.
How to restore, refresh, or reset your PC
http://windows.microsoft.com/en-US/windows-8/restore-refresh-reset-pc
Windows 8.1 Update Leaves OEM Owners With Broken Restore Function
Warning! If You Upgrade to Windows 8.1 Through Windows Store, You May Loose The Ability to Refresh and Reset
Update to Windows 8.1: FAQ
http://windows.microsoft.com/en-in/windows-8/upgrade-to-windows-8
Create installation media for Windows 8.1
http://windows.microsoft.com/en-us/windows-8/create-reset-refresh-media?ocid=tp_css_createmedia
Try contacting your OEM for the Windows 8 Recovery Media. For a small charge they should be able to supply you with a copy on DVD or USB. This will allow you to reinstall Windows 8 to factory settings as of day one.