VB.Net ขอคำแนะนำการตรวสอบวันที่หน่อยคับ มึนมาหลายชั่่วโมงแล้ว

If (Date_Start.Value.Date() > Date_Stop.Value.Date()) Then
          MsgBox("กรุณาระบุวันที่ให้ถูกต้อง")

        End If

 Private Sub BT_ADD_P_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BT_ADD_P.Click
        '=====DateTime_Start====='
        Dim years, days, dates_ST As String
        years = Date_Start.Value.ToString("yyyy") - 543 'change format year 2556-543 to 2013 
        days = Date_Start.Value.ToString("M-dd") 'chang format to Month-day
        dates_ST = years + "-" + days
        '=====DateTime_Stop====='
        Dim year, day, dates_FN As String
        year = Date_Stop.Value.ToString("yyyy") - 543 'change format year 2556-543 to 2013 
        day = Date_Stop.Value.ToString("M-dd") 'chang format to Month-day
        dates_FN = year + "-" + day


        Dim Test As Integer = 0
        Dim Test2 As Integer = 0
        Dim G As Integer
        Dim I As Integer
        'Dim TR As Integer

        With DataGrid_H

            For G = 0 To .Rows.Count - 1
                
                If ((TXT_ID_Pro.Text = .Rows(G).Cells(0).Value)) Then
                  

                    Dim M As Integer = CInt(TXT_Old_Price.Text)
                    Dim J As Integer = CInt(TXT_New_Price.Text)
                    Dim O As Integer = .Rows(G).Cells(4).Value
                    Dim F As Integer = CInt(TXT_DOnut_Amount.Text)
                    Dim P As Integer = CInt(TXT_Pro_Amount.Text)


                    TXT_Pro_Amount.Text = O + F
                    .Rows(G).Cells(4).Value = TXT_Pro_Amount.Text
                    .Rows(G).Cells(5).Value = TXT_New_Price.Text
                    Test = 1
                    Exit For
                End If

            Next
            If Test = 0 Then
                If (Date_Start.Value.Date() > Date_Stop.Value.Date()) Then
                    MsgBox("กรุณาระบุวันที่ให้ถูกต้อง")

                    DataGrid_H.Rows.Add(New String() {TXT_ID_Pro.Text, TXT_Pro_Name.Text, Date_Start.Text, Date_Stop.Text, TXT_Pro_Amount.Text, TXT_New_Price.Text})
                End If
            End If
        End With
        
        '+++++++++++++++++++ DataGrid_D +++++++++++++++++++++'
        With DataGrid_D
            For I = 0 To .Rows.Count - 1


                If ((Did_DN = .Rows(I).Cells(0).Value)) Then
                    Dim W As Integer = .Rows(I).Cells(2).Value
                    Dim X As Integer = CInt(TXT_DOnut_Amount.Text)
                    Dim Q As Integer
                    Q = W + X
                    .Rows(I).Cells(2).Value = Q
                    Test2 = 1
                    Exit For
                End If
            Next
            If Test2 = 0 Then
                DataGrid_D.Rows.Add(New String() {Did_DN, DonutName, TXT_DOnut_Amount.Text, TXT_Old_Price.Text})
            End If

        End With