To restart a service on a Windows machine using the command line, the 'net start' command followed by the service name is used to start a service that is stopped. In this case, the Print Spooler service is known as 'Spooler', hence 'net start Spooler' is the correct command. The 'sc start' command also starts services but 'sc restart Spooler' is incorrect because 'sc' does not support a direct 'restart' command without first stopping the service. 'services.msc' is not a command, but a Microsoft Management Console snap-in used for service management via a graphical interface, and 'net resume Spooler' is incorrect because 'net resume' is not a valid command for service management.