From the command prompt run this. Do you know the password for any of the accounts in the Administrators group? Does your account show up?
net localgroup administrators
I have tried to run 'net user administrator /active:yes' in admin powershell
If you were able to launch Powershell with "run as administrator", then you already have admin rights, By "root" do you really mean the SYSTEM account?
Update: From looking at the permissions on that folder, it would appear that you want to be "system". You can get a command prompt as that with PSExec.
psexec \\localhost -s cmd.exe
Be careful using that.