I have a Windows 10 Home machine (Lenovo Y520) with a Core i7-7700HQ processor. Windows 10 and the BIOS are up to date. So is Oracle Virtualbox.
Until recently it was running VMs just fine with Oracle Virtualbox (doing what I bought it to do). Then it stopped doing that. VirtualBox's New VM feature stopped offering me 64-bit VMs. The ones I already had in place stopped running.
I have tried the instructions in these answers:
Specifically, I've tried upating the BIOS, reloading BIOS default settings, turning on Intel Virtualization in the BIOS, rebooting, powering off and back on again, etc etc ad nauseam. W10 Home doesn't have the Microsoft virtualization features that often interferes with VirtualBox, and I've made sure Windows Hypervisor Platform is shut off.
Still, no 64-bit vms. What next?
VMWare Player gave a better diagnostic response than VirtualBox did when I tried to create a 64-bit virtual machine.
It said that my machine had the enterprise features Device Guard and Credential Guard enabled. I suppose they became enabled when I ran MalwareBytes; I can't think of any other change I made.
VMWare Player pointed me to a page called Manage Windows Defender Credential Guard. That page has a bunch of stuff about Group Policy Manager settings and the like, which of course are irrelevant to a W10 HOME installation.
In turn, that page pointed me to the Device Guard and Credential Guard hardware readiness tool, a PowerShell tool for enabling and disabling this feature set on servers.
Running that tool in a Run-As-Administrator power shell and giving this command
.\DG_Readiness_Tool_v3.5.ps1 -Disable -AutoReboot
took me through the process of disabling those features.
And I have virtualization capability back.