I recently was setting up a new Microsoft SharePoint 2010 machine and had promoted the machine to a domain controller before creating my SharePoint admin accounts.  I needed to add several of my accounts to the local Administrators group.  Unfortunately after you promote a server to a domain controller you can no longer access the GUI for Local Users and Groups.  Instead I had to use the command line to add the users.

Open a command promt using the “Run as administrator” function and then run the following command.

net localgroup Administrators /add {domain}{user}

eg: C:> net localgroup Administrators /delete MYDOMAINusername