Dim sUserName As String, sPassword As String, pstatus As String
        Dim nUserID As Integer, nUsername As String
//creating the mdi here 
        
Dim mdiform As New MDIparent()
        Dim cnn As SqlClient.SqlConnection = New SqlClient.SqlConnection(My.Settings.connectionstring)
        Dim adapter As SqlClient.SqlDataAdapter = New SqlClient.SqlDataAdapter
        Dim dt As New DataTable, strSQL As String

        Try
            sUserName = txtUserName.Text.Trim
            sPassword = txtPassword.Text.Trim

            If sUserName.Length = 0 Then
                MsgBox("You must enter a user name")
                txtUserName.Focus()
            ElseIf sPassword.Length = 0 Then
                MsgBox("You must enter a password")
                txtPassword.Focus()
            End If

            //code for login goes here 

                If pstatus = True Then
                    txtUserName.Focus()
                Else
                    My.Settings.UserID = nUserID
                    My.Settings.Username = sUserName
                    mdiform.Show()
                    Me.Close()
                End If
            Else
                MsgBox("Invalid username or password. Please try again")
                txtUserName.Focus()
            End If
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Login Error")
            txtUserName.Focus()
        End Try
        txtUserName.Text = ""
        txtPassword.Text = ""
    End Sub

//code for login goes here 

After successful login the Login Dialog Form return Ok , in either case it will return Cancel

//If the login is successfull open the mdi from 

 if(loginform.ShowDialog() == DialogResult.Ok)

	           My.Settings.UserID = nUserID
                   My.Settings.Username = sUserName
                   mdiform.Show()
ELSE
// If user click on Cancel exit form application
 Application.Exit(0);