Windows 8.1 Pro restarting in VirtualBox boot from ISO (virtualization enabled)

Question

I am trying to install Windows 8.1 Pro X86 on a VM with VirtualBox. My OS is LinuxMint 17 Cinnamon. Everything is set up properly except for the fact that I can't asign more than 1 CPU to it in settings. Not sure if it's because of this but when booting the VM from the ISO file I get an error and the VM keeps restarting.

http://www.sysprobs.com/guide-how-to-install-windows-8-1-on-virtualbox-guest-additions-download-iso-file

It is worth mentioning that I'm also getting an error when I first start the VM:

VT-x/AMD-V hardware acceleration is not available on your system. Certain guests (e.g. OS/2 and QNX) require this feature and will fail to boot without it.

While my issue is the same as this one, the difference is that my processor does support VT (link) and I do have it enabled in BIOS. My online searches have so far been fruitless and I'm starting to reach the end of the rope with this. Any help is greatly appreciated.

Edit: After reading another thread (link in comment) I've also tried the following changes in the BIOS but still nothing:

1. System Configuration > Device Configurations > Virtualization Technology <-- ENABLE this
2. System Configuration > Set Security Level > Data Execution Prevention <-- set to Change
3. System Configuration > Set Security Level > Virtualization Technology <-- set to Change

Answer 1

So as it turns out, after making these changes:

1. System Configuration > Device Configurations > Virtualization Technology <-- ENABLE this
2. System Configuration > Set Security Level > Data Execution Prevention <-- set to Change
3. System Configuration > Set Security Level > Virtualization Technology <-- set to Change

I also had to remove the laptop battery and leave it like that for awhile. After starting up the laptop again Windows finally booted from the ISO properly and I could continue with the installation.