To convert .VHDX to .VDI VirtualBox file in linux

You need to be VirtualBox installed, and the open Terminal into diretory where VHDX file is located and run

VBoxManage clonehd inputfile.VHDX outputfile.vdi --format VDI

And when the file is converted, import that file into VirtualBox

If that Windows is been into dual boot, you need to remove grub using lilo, like

How to remove grub using LILO

sudo apt-get update

sudo apt-get install lilo mbr

sudo lilo -M /dev/sda mbr

An another way to boot Windows is to use grub4dos iso

PS. Windows must be re-activate if it is used into VirtualBox.