ah. Now i found the Problem. I had the set the WindowState, Show the Form and Activate it. [Form.WindowState=FormWindowState.Normal; Form.Show(); Form.Activate();] The Problem occurs when you generate a hidden Winform on startup Subform blah = new Subform(); blah.Hide(); and then try to show it when the main Form is minimized private void button1_Click(object sender, System.EventArgs e) { this.WindowState = FormWindowState.Minimized; blah.WindowState = FormWindowState.Normal; blah.Show(); blah.Activate(); } It won't show up without bla.Activate();