Was not using VirtualBox for some time and now found that it stopped working (as usual).
When running, the following error appears
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}
SOLVED
It was a conflict with Hyper-V. When it is installed, then Oracle Virtual Box can't run 64-bit virtual machines.
Best Answer
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.