after installing ubuntu20.04.3 and restart, only a black screen, not the login window shows up

[abc12346]

Using VirtualBox-6.1.32-149290-Win, I successfully installed a VM using ubuntu-20.04.3-desktop-amd64.iso. However after it reboot, the ubuntu just show a black window. The login prompt never showed up. Attached is the log message. Can somebody tell me what could be wrong?
I tried to install Oracle_VM_VirtualBox_Extension_Pack-6.1.32 as well. In either case, the same problem.
Thank you.

[mpack]

00:00:02.184323 HM: HMR3Init: Attempting fall back to NEM: VT-x is not available
00:00:02.218492 NEM: info: Found optional import WinHvPlatform.dll!WHvQueryGpaRangeDirtyBitmap.
00:00:02.218550 NEM: WHvCapabilityCodeHypervisorPresent is TRUE, so this might work...

HMR3Init: Attempting fall back to NEM (Hyper-V is active).

You can't possibly have the "same problem" when installing the extension pack. The extension pack is not a VM. If that problem still exists after ditching Hyper-v then ask about it in a new topic.

p.s. The log file provided is not complete. In future please wait until the VM is fully closed down before grabbing the log, then zip the log to ensure it will fit here.

[abc12346]

Thanks for the reply. After doing the following 3 things, the green turtle becomes a blue "v", which I think means victory

1) bcdedit /set hypervisorlaunchtype off
2) set Local Computer Policy > Computer Configuration > Administrative Templates > System > Device Guard > Turn on Virtualization Based Security to Disabled
3) DISM /Online /Disable-Feature:Microsoft-Hyper-V #no sure if this is required

[scottgus1]

The blue V does in fact mean victory, or at least hardware Virtualization.

[mpack]

1) bcdedit /set hypervisorlaunchtype off
2) set Local Computer Policy > Computer Configuration > Administrative Templates > System > Device Guard > Turn on Virtualization Based Security to Disabled
3) DISM /Online /Disable-Feature:Microsoft-Hyper-V #no sure if this is required

The only thing missing from that list is a restart of the PC from a full power down state. Positive results may be temporary until the complete FAQ sequence is followed.