Haha, I tried the same and I didn't work.
Try this: Ehm, I forgot.
I'll try to find my old C# project and give you what I tried.
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This worked fine for me:
External_Overlay frm = new External_Overlay();
public Form1()
{
timer1.Start();
timer2.Start();
timer3.Start();
timer4.Start();
timer5.Start();
}