Error that i received while attempting to run Windows 8 ISO on VirtualBox before i could buy Windows 8 Pro. This happened with both 64 bit and 32 bit installations.

VT-x/AMD-V hardware acceleration has been enabled, but is not operational. Certain guests (e.g. OS/2 and QNX) require this feature.

Please ensure that you have enabled VT-x/AMD-V properly in the BIOS of your host computer.

Later i tried to run Ubuntu 12.0 64 Bit but it failed to run with error

This kernel requires a x86-64 cpu but only detected an i686 CPU. Unable to boot – please use a kernel appropriate for your CPU

It was caused as the VM was by default set to “Enable VT-x / AMD-V” Hardware Virtualization. This setting is visible by clicking on VM then Right Click > Settings > System > Acceleration