Failed to open a session for the virtual machine (VirtualBox)


Was not using VirtualBox for some time and now found that it stopped working (as usual).

When running, the following error appears

enter image description here

Some details

VT-d is enabled in BIOS

Host system is Windows 8

Version of

Text Version

Failed to open a session for the virtual machine Nebulla.

VT-x is not available. (VERR_VMX_NO_VMX).

Result Code: E_FAIL (0x80004005) Component: Console Interface: IConsole {db7ab4ca-2a3f-4183-9243-c1208da92392}


It was a conflict with Hyper-V. When it is installed, then Oracle Virtual Box can't run 64-bit virtual machines.

asked on Super User May 30, 2013 by Dims • edited May 31, 2013 by Dims

2 Answers


Even if you have all the virtualization BIOS settings enabled, if you have Hyper-V turned in on Windows Features, VirtualBox will not detect VMX as available.

Use "Turn Windows features on or off", if you are able to remove Hyper-V. If you are unable to live with that, perhaps you can migrate your VMs to Hyper-V.

answered on Super User May 5, 2015 by Andy Joiner

An efficient way to handle this is described in and it basically creates a boot option for launching your Windows environment without Hyper-V running by using 'bcdedit'.

bcdedit /copy {current} /d "Microsoft Windows – no hypervisor"
bcdedit /set {guid from the previous command} hypervisorlaunchtype off

Once you do that, reboot and you should see a menu at startup that lets you choose to boot with or without Hyper-V enabled. Works on Windows 10.

answered on Super User Jul 23, 2017 by Larry Smithmier

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