Start Task Manager by right-clicking the Taskbar, click the Performance tab
     and note the value for Uptime near the lower-right of the screen.
     - or -
     Run the following from a command prompt:
          systeminfo | find "System Boot Time:"
     The output will look something like this:
           System Boot Time: 11/12/2013, 1:23:45 AM


Här visas även installationsdatumet för OS