A few days ago I posted the solution to the error 0x000000C4 that you’ll run into if you try to install Windows Server 2012 R2 on VirtualBox. Now I just noticed that you get the same error message when you install Windows 8.1 Preview on VrtualBox:
Your PC needs to restart.
Please hold down the power button.
Error code: 0x000000C4
Parameters:
0×0000000000000091
0x000000000000000F
0xFFFFF801E5962A80
0×0000000000000000
The solution to the problem is the same as for Windows Server 2012 R2:
"c:\Program Files\Oracle\VirtualBox\VBoxManage.exe" setextradata [vmname] VBoxInternal/CPUM/CMPXCHG16B 1
Replace vmnmae with the name of the virtual machine name which you can find in the VirtualBox Manager. Put the vname in quotes if contains blanks.
The problem exists only with the Windows 8.1 64-bit. The 32-bit version works fine.