I know this thread is a little dated but here goes...
I'm curious, why not build a new VM from scratch, dcpromo it to a domain controller then dcpromo (demote) the original one?
This may not be what you're looking for but it should be a lot easier and less risky, especially if you only have one DC.
Note, make sure you transfer the FSMO roles to the new DC before you shut down the old one. You must be an Enterprise Admin & Schema Admin, here's how to seize the roles:
Open a command prompt and run ntdsutil. In the following steps, each line is a separate command, type:
roles
connections
connect to server <SERVERNAME>
quit
seize pdc
seize rid master
seize schema master
seize infrastructure master
seize domain naming master
quit
quit
You also need to make sure the new DC is in the correct site and that it's a Global Catalog server in AD Sites and Services / Sites / <SITE NAME> /
Servers / <SERVERNAME> / NTDS Settings / Properties
......... ok, maybe this isn't the simplest process and the are a few "gotchas" but at least you can leave you're old DC intact until you prove to yourself that the new one is stable.