VT Not Supported when Installing HAXM
So the only solution I've found to make it work is to completely disable Hyper-V in Control Panel -> Programs and Features -> Turn Features On or Off.
If anyone knows how to enable VT-x without disabling Hyper-V please answer this question...
To turn off Hyper-V run this from cmd: bcdedit /set hypervisorlaunchtype off, and then reboot.
To turn Hyper-V back on, run this: bcdedit /set hypervisorlaunchtype auto
I had the same problem and I just found, that in Avast 9 there is an option to prevent it from using the virtualization feature. It has some impact on the Avast Sandbox, but after I disabled it, I could finally install HAXM.