login on vb;username password at ms access

[cicatrix]

This example provides you have an access database with a table named USERS having fields USERID and PASSWORD in it. Also you must have a connection string to your database.

In your main form you will need to call frmLogin:

Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal As System.EventArgs) Handles btnLogin.Click
     Dim frm As New frmLogin
     Dim ret As DialogResult = frm.ShowDialog()
     If ret <> Windows.Forms.DialogResult.OK Then
         MsgBox("Login failed", MsgBoxStyle.Exclamation)
     Else
         ' Logged in
     End If
End Sub

Now you should create a frmLogin having txtLogin and txtPassword (textboxes) and btnLogin (a button):

Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal As System.EventArgs) Handles btnLogin.Click
        ' Create a connection to your database:
        Dim conn As New OleDbConnection("your connection string goes here")
        ' Create a query string (with parameters):
        Dim sql As String = "SELECT USERID FROM USERS WHERE USERID=@p_userid AND PASSWORD=@p_passw;"
        Dim cmd As New OleDbCommand(sql, conn)
 
        ' Add parameters
        With cmd
            .Parameters.AddWithValue("p_userid", txtLogin.Text)
            .Parameters.AddWithValue("p_passw", txtPassword.Text)
        End With
 
        ' Open your connection and perform the query
        Try
            conn.Open()
            Dim usr As String = cmd.ExecuteScalar.ToString
            If Not (IsDBNull(usr)) AndAlso usr = txtLogin.Text Then
                Me.DialogResult = Windows.Forms.DialogResult.OK   ' Return OK (user is found password matches)
            Else
                Me.DialogResult = Windows.Forms.DialogResult.Cancel ' Return Cancel (query returned nothing)
            End If
        Catch ex As Exception
            ' Catch database connection or query errors:
            MsgBox("Could not connect to database or database error." & Environment.NewLine &
                    "Error message:" & ex.Message)
            Me.DialogResult = Windows.Forms.DialogResult.Cancel
        Finally
            ' Close connection
            conn.Close()
            Me.Close()
        End Try

This is a very simple mechanism which provides almost no security at all since usernames and passwords are stored in unencrypted forms and the database itself can be compromised.