We were installing a small bit of backup software that we use regularly on a 2008R2 server when, for no apparent reason, the screen went blank during the install and then we came back to the logon screen.

Since that we are unable to logon to either the DC or any other domain member machine with a domain admin level account. All normal user accounts are working fine and can access files. All group policies seem to be working etc.

The only thing i can find is people saying to use the AD restore mode but I can almost guarantee that the company doesn't know what the restore mode password is.

Any clue would be helpful!!