Hi! I am Not able to Update database through Datagridview in VB.net Pls help

Private Sub btnUpdate_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnUpdate.Click

        Dim str As String

        If Not cnn.State = ConnectionState.Open Then

            cnn.Open()

        End If

        If Me.txtID.Text & "" = "" Then

            cmd.Connection = cnn

            cmd.CommandText = "INSERT INTO CLIENT_REGISTER(CLIENTID,NAME,ADDRESS,PHONE,MOBILE) VALUES ('" & Me.txtID.Text & "','" & Me.txtName.Text & "','" & Me.txtAddress.Text & "','" & Me.txtPhone.Text & "','" & Me.txtMobile.Text & "')"

            cmd.ExecuteNonQuery()

        End If

        cmd.Connection = cnn

        str = "UPDATE CLIENT_REGISTER SET NAME='" & Me.txtName.Text & "',ADDRESS='" & Me.txtAddress.Text & "',PHONE='" & Me.txtPhone.Text & "',MOBILE='" & Me.txtMobile.Text & "' WHERE CLIENTID=" & Me.txtID.ReadOnly

        cmd = New OleDbCommand(str, cnn)

        cmd.ExecuteNonQuery()

        RefreshData()

        cnn.Close()

        VEnable()

        Me.btnSave.Enabled = False

        Me.btnEdit.Enabled = False

        Me.btnUpdate.Enabled = False

        Me.btnCancel.Enabled = True

        Me.btnNew.Enabled = True

End Sub