It has taken me a while to figure this out. After Googling for about half an hour, it seems that the message in error log does help pointing into the right direction.
HWACCM: VMX setup failed with rc=VERR_VMX_IN_VMX_ROOT_MODE!
Let me first briefly state the problem, I have been using VirtualBox with no problem, until recently that I have upgraded to newest version of virtualbox and got nothing working like before.
At last, it was not any issue with the update, but rather the installed Intel VM Hypervisor to help accelerating my android emulation. After uninstalling the Intel’s stuff (using instruction described in the installation page of the software package) my VirtualBox returned to its working condition.
Hope this post helps saving you at least few minutes of googling ; )