Visual Basic数据库和注册表单

Question

这是我第一次做VB。我已成功创建登录表单，但我遇到了用户注册问题。我点击注册的那一刻，它给出了数据库连接失败并且无法插入注册的错误。请帮忙。 提前致谢

If rtxtpassword.Text = "" Or rtxtusername.Text = "" Or rtxtfname.Text = "" Or rtxtlname.Text = "" Then
            MessageBox.Show("Please complete the required fields..", "Authentication Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Else
        End If

        ' Connect to DB
        Dim conn As New System.Data.OleDb.OleDbConnection()
        conn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\logan_000\documents\visual studio 2013\Projects\Point Of Sale Application\Point Of Sale Application\database.accdb"

        Try
            'Dim sql As String = "INSERT INTO Registration WHERE username='" & rtxtusername.Text & "' AND Password = '" & rtxtpassword.Text & rtxtfname.Text & "' AND Fname = '" & rtxtlname.Text & "' AND Lname =  '"
            Dim sql As String = "INSERT INTO Registration (username, Password, Fname, Lname) VALUES (" & rtxtusername.Text & ", " & rtxtpassword.Text & ", " & rtxtfname.Text & ", " & rtxtlname.Text & ")"
            'Dim sql As String = "INSERT INTO Registration (username, Password, Fname, Lname) VALUES('" & rtxtusername.Text & "'," & "'" & rtxtpassword.Text & "',"
            Dim sqlCom As New System.Data.OleDb.OleDbCommand(Sql)

            'Open Database Connection
            sqlCom.Connection = conn
            conn.Open()
            Dim sqlRead As System.Data.OleDb.OleDbDataReader = sqlCom.ExecuteReader()

            If sqlRead.Read() Then
                Form1.Show()
                'Me.Hide()
                Me.Close()
            Else
                ' If user enter wrong username and password combination
                ' Throw an error message
                MessageBox.Show("Registration Failed..", "Authentication Failure", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)

                'Clear all fields
                rtxtusername.Text = ""
                rtxtfname.Text = ""
                rtxtlname.Text = ""
                rtxtpassword.Text = ""

                'Focus on Username field
                rtxtusername.Focus()
            End If
            'Connection failure Dialog box
        Catch ex As Exception
            MessageBox.Show("Failed to connect to Database.. System Error Message:  " & ex.Message, "Database Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try

    End Sub