Updating SQL table from datagridview

I have an SQL query linked to a datagridview.

I can update / delete data etc using single sql statements bt when i try to do it by simply put data in the datagrid view table i get the following error.

"Update requires valid UpdateCommand when passed datarows with modified data rows"

This is what fails on the form close event.......

Imports System.Data.SqlClient

Public Class Form1
    ' Shared variables
    Dim con As SqlConnection = New SqlConnection("Server=.\SQLEXPRESS;Database=OEE;USER Id=Alan Sweeting;Trusted_Connection=True")
    Dim cmd As SqlCommand
    Dim myDA As SqlDataAdapter
    Dim myDataSet As DataSet

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        'Binding database table to DataGridView
        cmd = New SqlCommand("Select * FROM qry_Stops", con)
        If con.State = ConnectionState.Closed Then con.Open()
        myDA = New SqlDataAdapter(cmd)
        myDataSet = New DataSet()
        myDA.Fill(myDataSet, "qry_Stops")
        DataGridView1.DataSource = myDataSet.Tables("qry_Stops").DefaultView

    End Sub

Private Sub Form1_FormClosed(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles MyBase.FormClosed
        'update records
        Me.Validate()
        myDA.Update(myDataSet.Tables("qry_Stops"))
        myDataSet.AcceptChanges()
        con.Close()
        con = Nothing
    End Sub
End Class

I tried seperately with a simple update line and that works fine when i know what is updated but in the case i don;t know what is going to be changed and on which row.

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

        'update record
        cmd = New SqlCommand("Update qry_Stops Set [DowntimeCode]=1 Where [DowntimeDescription]='Mech'", con)
        If con.State = ConnectionState.Closed Then con.Open()
        cmd.ExecuteNonQuery()
        ShowStops() 'Rebinding to DataGridView and view result

    End Sub

Public Sub ShowStops()

        'Binding database query to DataGridView
        cmd = New SqlCommand("Select * FROM qry_Stops", con)
        If con.State = ConnectionState.Closed Then con.Open()
        myDA = New SqlDataAdapter(cmd)
        myDataSet = New DataSet()
        myDA.Fill(myDataSet, "qry_Stops")
        DataGridView1.DataSource = myDataSet.Tables("qry_Stops").DefaultView

    End Sub

I am a total novice so please don't pass me to another link, i need someone to explain to me what i am doing wrong.

Thankyou