I don't have any other virtualization technology running on this machine (that I'm aware of) - I verified Hyper-V was not enabled as a feature in the OS, and I don't have anything from VMware or other such technology running on this. Unable to boot - please use a kernel appropriate for your CPU.' 'This kernel requires an x86-64 CPU, but only detected an i686 CPU. On attempting to boot off the 64-bit Ubuntu 13.10 desktop ISO media (I also tried 13.04 64-bit), I get this message before it gets far in the boot process at all (before any prompts for me to interact with it while it's still loading off the ISO media: In spite of setting up things as I did on my old system where I could run 64-bit guests fine with more than one CPU, this one stone walls me. I also setup the usual stuff I have in the past with my older machine (was a Core i7-920) regarding guest system options such as VT-x, Nested Paging and PAE/NX. I setup an Ubuntu guest and gave it 4GB RAM and 2 CPUs. The motherboard does have virtualization enabled in the BIOS-I double checked that. The hardware is an ASUS Maximus VI Hero with 16GB RAM installed and a Core i7-4770k processor. I hadn't tried to install VirtualBox on this particular new hardware prior to upgrading to 8.1, but it did install fine as well as the VirtualBox extensions. I installed VirtualBox 4.3.0 r89960 onto a machine I recently built (and also upgraded to Windows 8.1 Pro from 8 Pro).

Virtualbox windows 8.1 32 bit