This isn't a network issue. It belongs in the server sub forum.
Anyways, there is no such thing as restoring to "factory defaults" for a server OS. If this server was part of a domain, you need to hope someone had logged on to the server with the admin user you have the password for. That's if this is the domain admin account. If it is the local admin account to the server and this a non-AD server, you have to specify to the server OS this is a login using a local server account. To do this, you have to enter [machine/server name]\[local user account] instead of using just the user account.
Anyways, there is no such thing as restoring to "factory defaults" for a server OS. If this server was part of a domain, you need to hope someone had logged on to the server with the admin user you have the password for. That's if this is the domain admin account. If it is the local admin account to the server and this a non-AD server, you have to specify to the server OS this is a login using a local server account. To do this, you have to enter [machine/server name]\[local user account] instead of using just the user account.