ตัว update กับ delete ของผมไม่ทำงานอ่ะครับ แต่ insert กลับได้ครับ

Imports System.Data
Imports System.Data.OleDb
Imports System.Configuration
Public Class database
    Private con As OleDbConnection
    Private cmd As OleDbCommand
    Private strconstring As String

    Public Sub New()
        strconstring = System.Configuration.ConfigurationManager.ConnectionStrings("Chase.My.MySettings.chaseConnectionString").ConnectionString
    End Sub

    Public Function querydataset(ByVal strsql As String) As DataSet
        Dim ds As DataSet
        Dim da As New OleDbDataAdapter
        con = New OleDbConnection
        With con
            .ConnectionString = strconstring
            .Open()
        End With
        cmd = New OleDbCommand
        With cmd
            .Connection = con
            .CommandType = strsql
            .CommandType = CommandType.Text
        End With
        da.SelectCommand = cmd
        da.Fill(ds)
        Return ds
    End Function

    Public Function queryexecute(ByVal strsql As String) As Boolean
        con = New OleDbConnection
        With con
            .ConnectionString = strconstring
            .Open()
        End With
        Try
            cmd = New OleDbCommand
            With cmd
                .Connection = con
                .CommandType = CommandType.Text
                .CommandText = strsql
            End With
            cmd.ExecuteNonQuery()
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function

End Class

Imports System.Data
Imports System.Data.OleDb
Public Class Form2

    Dim clsdb As New database

    'Dim fcon As New Main
    'Dim con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\User\Desktop\Chase\Chase\Chase\bin\Debug\chase.mdb")
    'Dim cmd As New OleDbCommand

    Sub showdata()
        On Error Resume Next

        Dim sql As String = "select sid as รหัสพนักงาน,sname as ชื่อพนักงาน,stel as หมายเลขติดต่อ from staff "
        Dim ds As DataSet
        ds = clsdb.querydataset(sql)
        DataGrid1.DataSource = ds.Tables(0)
        'Dim ds As New DataSet
        'Dim da As New OleDbDataAdapter

        'da = New OleDbDataAdapter(sql, con)
        'da.Fill(ds, "s")
        'DataGrid1.DataSource = ds.Tables("s")

    End Sub

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'On Error Resume Next
            showdata()
            clear()

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ' fcon.connect()
        Dim sql As String = "insert into staff values('" & TextBox1.Text & "','" & TextBox2.Text & "','" & TextBox3.Text & "')"
        'con.Open()

        'With cmd
        '    .CommandText = sql
        '    .CommandType = CommandType.Text
        '    .Connection = con
        '    .ExecuteNonQuery()

        'End With
        'con.Close()
        'MsgBox("OK")
        If clsdb.queryexecute(sql) = True Then
            MsgBox("OK")
        End If
        showdata()
        clear()
        clsdb.close()

    End Sub

    Sub clear()
        TextBox1.Text = ""
        TextBox2.Text = ""
        TextBox3.Text = ""
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim sql As String = "update staff set sname='" & TextBox2.Text & "',stel='" & TextBox3.Text & "' where sid='" & TextBox1.Text & "'"
        'con.Open()

        'With cmd
        '    .CommandText = sql
        '    .CommandType = CommandType.Text
        '    .Connection = con
        '    .ExecuteNonQuery()

        'End With
        'con.Close()
        'MsgBox("OK")
        If clsdb.queryexecute(sql) = True Then
            MsgBox("OK")
            TextBox1.ReadOnly = False
            showdata()
            clear()
            clsdb.close()
        Else
            MsgBox("ไม่สารถแก้ไขได้")
        End If

    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim sql As String = "delete from staff where sid='" & TextBox1.Text & "'"
        'con.Open()

        'With cmd
        '    .CommandText = sql
        '    .CommandType = CommandType.Text
        '    .Connection = con
        '    .ExecuteNonQuery()

        'End With
        'con.Close()
        'MsgBox("OK")
        If clsdb.queryexecute(sql) = True Then
            MsgBox("OK")
        End If
        showdata()
        clear()
        clsdb.close()
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Dim sql As String = "select * from staff where sname='" & TextBox2.Text & "' "
        Dim ds As DataSet
        ds = clsdb.querydataset(sql)
        TextBox1.Text = ds.Tables(0).Rows(0)("sid")
        TextBox2.Text = ds.Tables(0).Rows(0)("sname")
        TextBox3.Text = ds.Tables(0).Rows(0)("stel")
        TextBox1.ReadOnly = True
        clsdb.close()
    End Sub
End Class