can't update table

[tolisss]

i m using the following code without errors but the data in the table remains the same what i m doing wrong

da = New OleDbDataAdapter("SELECT * FROM t", cnNew)
        ds = New DataSet("t")
        da.Fill(ds, "t")
        For Each drRow In ds.Tables.Item("t").Rows
            drRow.Item("LastN") = "test"
        Next
        ds.AcceptChanges()
        Try
            da.Update(ds, "t")
        Catch ex As Exception
            Trace.WriteLine(ex.Message)
        End Try