ASP.NET - Problemas con DataGridView

Dim Alumnos(7) As Alumnos

        Dim Notas(3) As Notas

        Dim sum As Integer = 0

        Dim Tamaño As Integer

        Tamaño = Convert.ToInt32(InputBox("Cuantos Alumnos va a agregar", "Ingreso de ALumnos"))

        Array.Resize(Alumnos, Tamaño)

        For i As Integer = 0 To Alumnos.GetUpperBound(0)

            Alumnos(i).Nombre = Convert.ToString(InputBox("Nombre del Alumno(a) : ", "Información Personal"))

            MessageBox.Show("Tendrá que Agregar 4 Notas", "Notas", MessageBoxButtons.OK, MessageBoxIcon.Information)

            Notas(0).Notas = InputBox("Nota 1: ", "Notas")

            Notas(1).Notas = InputBox("Nota 2: ", "Notas")

            Notas(2).Notas = InputBox("Nota 3: ", "Notas")

            Notas(3).Notas = InputBox("Nota 4: ", "Notas")

            For m As Integer = 1 To 5

                For j As Integer = 0 To DataGridView1.Rows.Count

                    sum = (DataGridView1.Rows(m).Cells(j).Value)

                Next

                sum = DataGridView1.Rows(m).Cells(4).Value + sum

                DataGridView1.Rows(m).Cells(5).Value = sum

                TextBox1.Text = (sum)

            Next

            DataGridView1.Rows.Add(Alumnos(i).Nombre, Notas(0).Notas, Notas(1).Notas, Notas(2).Notas, Notas(3).Notas, sum)

        Next

    End Sub

For m As Integer = 1 To 5

For j As Integer = 0 To DataGridView1.Rows.Count

sum = (DataGridView1.Rows(m).Cells(j).Value)

Next

sum = DataGridView1.Rows(m).Cells(4).Value + sum DataGridView1.Rows(m).Cells(5).Value = sum TextBox1.Text = (sum) Next