Problem with form login in Access 2007

[Lilian]

Hi,
I did an login form to my database and get some problem with VBA code.
I used a combox with names of employees and get problem with this.
Everything is working when I choose some name from this combobox but when
not choose I don't get warning message that missed to write a username.
One more problem when I am trying to write password more then 3 times I
don't quit from the database.
Please, help me!
Lilian
Here is the code
Private Sub cmdLogin_Click()


If IsNull(Me.cboEmployee) Or Me.cboEmployee = "" Then
MsgBox "You must enter a User Name.", vbOKOnly, "Required Data"
Me.cboEmployee.SetFocus
Exit Sub
End If

'Check to see if data is entered into the password box

If IsNull(Me.txtPassword) Or Me.txtPassword = "" Then
MsgBox "You must enter a Password.", vbOKOnly, "Required Data"
Me.txtPassword.SetFocus
Exit Sub
End If

'Check value of password in tblEmployees to see if this
'matches value chosen in combo box

If Me.txtPassword.Value = DLookup("strEmpPassword", "tblEmployees", _
"[lngEmpID]=" & Me.cboEmployee.Value) Then

lngMyEmpID = Me.cboEmployee.Value

'Close logon form and open splash screen

DoCmd.Close acForm, "frmLogon", acSaveNo
DoCmd.OpenForm "frmSplash_Screen"

Else
MsgBox "Password Invalid. Please Try Again", vbOKOnly, _
"Invalid Entry!"
Me.txtPassword.SetFocus
End If

'If User Enters incorrect password 3 times database will shutdown

intLogonAttempts = intLogonAttempts + 1
If intLogonAttempts > 3 Then
MsgBox "You do not have access to this database.Please contact
admin.", _
vbCritical, "Restricted Access!"
Application.Quit
End If

End Sub