[Solved] Windows 10 1803 - VT-x is not available

[socratis]

Upgraded to 1803 a little while back. VirtualBox was working fine. Did a reboot today and am now getting a "VT-x is not available" when trying to start VMs.

Hyper-V is off.
WMI "select * from Win32_ComputerSystem" returns HypervisorPresent = True

Enabled Hyper-V, rebooted, disabled Hyper-V, rebooted. No change.
Added "EnableVirtualizationBasedSecurity" reg key, set it to 0, rebooted, no change.

Has anyone else run into this?

[socratis]

Did you re-install VirtualBox?
I need the exact error message. VT-x is not available is not the same as Hyper-V is in use.

[s-jones]

Yes, I did an uninstall / reinstall of VirtualBox.

Failed to open a session for the virtual machine Windows 10.

VT-x is not available (VERR_VMX_NO_VMX).

Result Code: E_FAIL (0x80004005)
Component: ConsoleWrap
Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

[socratis]

Please go thoroughly through the FAQ: I have a 64bit host, but can't install 64bit guests.

Those are guidelines, you have to use your judgement, don't expect the solution to pop out...

[s-jones]

This fixed it:

Local Computer Policy > Computer Configuration > Administrative Templates > System > Device Guard > Turn on Virtualization Based Security to Disabled

[socratis]

Great! Thanks for the feedback. Marking as [Solved].

[s-jones]

Thanks for the pointer to the article. It was just very odd that it worked for about a week and a half before "breaking".

[socratis]

Microsoft acts like one of those protective "mothers" that knows what's best for you, no matter if you want it or not...

[LiamH]

After a recent administrator update of Windows 10 host OS I found that I could not start up the guest OS; I got exactly this message. It had been working for nearly a year previous to this update. I was able to resolve it following these instructions; I had to change two settings. For the benefit of those who like me know little to nothing about configuring Windows, I'm giving my complete steps.

1. 4 panes (lower left)-> Gear (upper right "common utilities") -> Magnifying glass type "Group policy" -> Edit group policy -> following steps in MS documentation, set "Turn on Virtualization Based Security" to "Disabled" (it was set to "Enabled").
2. Follow instructions here to disable Hyper-V by clicking on box filled black so that the fill was removed.
3. Restart Windows

After that I was able to start up VBox and the guest OS as before without problem.

[MyselfGr]

That thing drived me paranoid....

Searched everywhere for a solution but after few hours of trying and fail i came across someone mentioning about

Core Isolation is enabled

Which was the source of my headache.

Turned it off and VOILA...problem solved