FormClosing shutdown event doesnt write to a file

I have a backup power supply for my computer which is attacted inline with it and the wall. When I pull the power cord from the wall, I have 2-5 minutes before the backup supply shuts down the computer. It is during this time that I want to write data to a file with the code below:

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
     {
         if (e.CloseReason.Equals(CloseReason.WindowsShutDown))
         {
             writeContents("Interrupted");
             sendMessage("PWR - The Spring Test Machine has stopped");                return;
 
         }
 
 
 
         if (e.CloseReason.Equals(CloseReason.UserClosing)) 
         {
             if (MessageBox.Show("You are closing this application.\n\nAre you sure you wish to exit ?", "Warning: Not Submitted", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Stop) == DialogResult.Yes)
             {
                 writeContents("Interrupted");
                 return;
             }
 
             else
                 e.Cancel = true; 
         } 
 
     }
 

The problem is that it didn't work. I dont think the the closing event ever got called. Any ideas would greatly be appreciated. Thank you.

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