envoke different form with a timer

Hi everyone! I've got a form in which a timer is running. This timer shall show one of 3 different forms in a alternating sequence. my problem: If a form is envoked by a timer, it will not be drawed onto the screen. Which makes my programm quite useless ... I've already found somthing that this can be solved with Application.DoEvents(); However, this method doesn't seem to work. Usually this method tells the application to finish window operations which have not been done yet. Could anyone help me with that great thanks