You should be starting from a Sub Main which checks the type and loads just only the one form that is needed. Sub Main can be in a class or a Module and set it as the start point from the project properties. You also have to show the form modally or call Application.Run after it so the application knows to stay open. Something like this:
VB Code:
Public Module StartUp
Public Sub Main()
Dim auth As String=GetAuthClass
Select Case auth
Case "Admin"
Application.Run(New frmHighLevel)
Case "Other"
Application.Run(New frmMidLevel)
Case Else
Application.Run(New frmLowLevel)
End Select
End Sub
End Module