update: VirtualBox  6.1 is supporting working on Windows 10 with HyperV enabled.

I tried to run my VirtualBox machine and got this message :

VT-x/AMD-V hardware acceleration is not available on your system. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot.

I made sure that I have VT-x enabled in BIOS I still getting the same error ; and after some investigation  I found that I have installed Microsoft Hyper-V to run Android emulator with Visual Studio 2015 and that Hyper-V lock the hyper-visor feature of my CPU and windows loading.

As I don't want to uninstall Hyper-V and search and came up to a solution which is have to boot configuration for my PC , one with Hyper-V enabled and one disables so I can run 64-bit gust machine in VirtualBox .

The solution :

Open an administrative command prompt and run:

C:\>bcdedit /copy {current} /d "Windows with HyperV"
C:\>bcdedit /set hypervisorlaunchtype off