Works starting with windows XP, not available in win 2000 or lower:
This is the quickest way to do it:
Process.Start("shutdown","/s /t 0");
Otherwise use P/Invoke or WMI like others have said.
Edit: how to avoid creating a window
var psi = new ProcessStartInfo("shutdown","/s /t 0");
psi.CreateNoWindow = true;
psi.UseShellExecute = false;
Process.Start(psi);
thanks to Pop Catalin
.net - How to shut down the computer from C# - Stack Overflow[
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