I was having a lot of trouble booting up on Windows 8.1 with my Gigabyte X99 UD4 motherboard. The solution is fairly easy to implement:
1. Insert your Windows 8 (or 8.1) disk into your dvd drive and restart pc.
2. At boot screen, push F12 to go to boot device selection menu and select UEFI DVD Drive.
3. Windows 8 will boot to Windows 8 Install screen
4. Select "Repair your Computer" option.
5. Light Blue Screen will appear shortly, select "Trouble Shooting"
6. Select "Advanced"
7. Push F1 button to select: Put Windows 8 in Debugging Mode.
8. Push finish or enter button. Remove Windows 8 disc.
9. Reboot PC.
Problem solved! Computer does not hang on Windows Bios Boot Screen.
