Second Hand PCs What To Connect To Non Existent Old Domain?

I have 6 PCs which I got off a friend who wound up his business. The machines are set up to logon to the old now none existent domain.When I switch on the machines the typical set up is this

CS-PC08
password:

I have no passwords, Switch user, none available, I do have an option to log on to another domain.

To Logon to another domain enter domainuser

To Logon locally it says, enter CS-PC08local user name

I have no password or user names.I cannot boot in safe mode or in safe mode with command prompt without encountering a logon screen.I have downloaded Password Unlocker and whilst this allows me to change passwords and add users I still get the same logon screen and none of my new user names or changed passwords help.I have no disks so cant do a reinstall.