Modules & VBA :: Search And Validate For Login Form

I have a table called 'Klanten' which contains the rows 'password' and 'login' (and several rows not needed for this form)

So I'm trying to make a login form which first checks if something is entered (this part of the code seems to work).

Private Sub Knop13_Click()
'Check to see if data is entered into Username
If IsNull(Me.Username) Or Me.Username = "" Then
MsgBox "gelieve een login in te voeren.", vbOKOnly, "Required Data"
Me.Username.SetFocus

[Code] ....

But from then on i seem to have some issues.. The part of the code underneath seems to only work for the first 'login' and 'paswoord' in my table called "Klanten".

-Username is the name for the field where they enter their 'login'.
-Password is the name for the field where they enter their 'paswoord'

If Username.Value <> DLookup("[login]", "Klanten", "[Username]='" & Username & "'") Then
MsgBox "Invalid Username. Please try again.", vbOKOnly, "Invalid Entry!"
Exit Sub
End If

If Password.Value <> DLookup("[wachtwoord]", "Klanten", "[Password]='" & Password & "'") Then
MsgBox "Invalid Password. Please try again.", vbOKOnly, "Invalid Entry!"
Exit Sub
End If

Then as last part i would like to goto another form called 'Mainmenu' if both the Login and the Paswoord is correctly entered in the fields Username and Password. Here i have the most issues as this doesn't seem to do anything at the moment

If Password.Value = DLookup("[wachtwoord]", "Klanten", "[Username]='" & Username & "'") And Username.Value <> DLookup("[login]", "Klanten", "[Password]='" & Password & "'") Then DoCmd.OpenForm "Mainmenu"
End Sub