Welcome to the Community,
hot (powered on) converting a DC is not supported, and in most cases causes issues with the AD. The recommended way to move the AD to a virtual machine is to create a new virtual server, promote it to a DC, migrate the FSMO roles, and then demote the physical server.
What I've done in the past - although not officially supported - is to convert a powered off DC using the ColdClone CD (which unfortunately isn't available for download anymore).
You can also find other options on the Internet, like MOA or booting the physical host from a Linux Live CD, make it an iSCSI target, mount the server's disks as RDMs and then migrate/copy the RDMs to virtual disks.
André