Unable to bring opened form to front/focus vb.net

Hi i have five forms and i want to open a form only if it's not open, if it's open bring to front or focus. i have tried using BringToFront,Show and TopMost but nothing works.

If Not Application.OpenForms.OfType(Of StudentRegistrationFrm).Any Then
        StudentRegistrationFrm.ShowDialog()
    Else
        StudentRegistrationFrm.BringToFront()
        'Me.SendToBack()
    End If