//SHUT DOWN
protected void btnShutDown_Click(object sender, EventArgs e)
{    
 Process.Start("shutdown.exe", "-s");
 // By Default the Shutdown will take place after 30 Seconds
 //if you want to change the Delay try this one
 Process.Start("shutdown.exe","-s -t xx");
 //Replace xx with Seconds example 10,20 etc
}

//RESTART
protected void btnRestart_Click(object sender, EventArgs e)
{
 Process.Start("shutdown.exe", "-r");
 // By Default the Restart will take place after 30 Seconds
 //if you want to change the Delay try this one
 Process.Start("shutdown.exe","-r -t 10");
 //Replace xx with Seconds example 10,20 etc
}

// LOG OFF
protected void btnLogOff_Click(object sender, EventArgs e)
{
 Process.Start("shutdown.exe", "-l");
 //This Code Will Directly Log Off the System Without warnings
}