Hola, este codigo es para cambiar la frecuencia del monitor

Código:
Option Explicit
Private Declare Function EnumDisplaySettings Lib "user32" Alias "EnumDisplaySettingsA" (ByVal lpszDeviceName As Long, ByVal iModeNum As Long, lpDevMode As Any) As Boolean
Private Declare Function ChangeDisplaySettings Lib "user32" Alias "ChangeDisplaySettingsA" (lpDevMode As Any, ByVal dwflags As Long) As Long

Const CCDEVICENAME = 32
Const DM_DISPLAYFREQUENCY = &H400000
Const CCFORMNAME = 32

Private Type DEVMODE
  dmDeviceName As String * CCDEVICENAME
  dmSpecVersion As Integer
  dmDriverVersion As Integer
  dmSize As Integer
  dmDriverExtra As Integer
  dmFields As Long
  dmOrientation As Integer
  dmPaperSize As Integer
  dmPaperLength As Integer
  dmPaperWidth As Integer
  dmScale As Integer
  dmCopies As Integer
  dmDefaultSource As Integer
  dmPrintQuality As Integer
  dmColor As Integer
  dmDuplex As Integer
  dmYResolution As Integer
  dmTTOption As Integer
  dmCollate As Integer
  dmFormName As String * CCFORMNAME
  dmUnusedPadding As Integer
  dmBitsPerPel As Integer
  dmPelsWidth As Long
  dmPelsHeight As Long
  dmDisplayFlags As Long
  dmDisplayFrequency As Long
End Type
Dim Dispositivo As DEVMODE

Sub Cambiar_Frecuencia(Frecuencia As Single)
  Dim a As Boolean
  Dim i As Integer
  i = 0
  Do
    a = EnumDisplaySettings(0&, i, Dispositivo)
    i = i + 1
  Loop Until (a = False)

  Dim b&
  Dispositivo.dmFields = DM_DISPLAYFREQUENCY
  Dispositivo.dmDisplayFrequency = Frecuencia

  ChangeDisplaySettings Dispositivo, 0
End Sub

Sub Form_Load()
Call Cambiar_Frecuencia(60)
End Sub
le pasan como valor a la funcion la frecuencia en Hz que quieren ponerle.

saludos.