Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If TextBox1.Text = "user" And TextBox2.Text = "user" Then
            Form2.Show()
        ElseIf TextBox1.Text <> "senha" Or TextBox2.Text <> "senha" Then
            MsgBox("Usuario e/ou senha inválidos.")
        End If
    End Sub
End Class