I had/have the same problem. It happens when the BCLK is set over 100. I manually changed this to 100 and the double boot went away.
Edit: just saw your comment about getting into bios. I assume that you tried pressing del when the computer boots? Or F8? Just spam either one when you boot.
Once you get into bios, choose the "exit/advanced" option at the top right corner. Then advanced mode option. Select AI Tweaker and select Ai overclock tuner and set to "manual". The select BCLK/PCIE Frequency and enter "100.0".
Should solve your issue.
On a secondary note, you may also run into a problem where your mobo won't wake from sleep mode. The computer will seem like it is waking, but no video and no mouse/keyboard will work. If this happens, go into Bios, Advanced Mode, AI Tweaker and disable Internal PLL Overvoltage.
Worked for me anyway. Good Luck!