[Modestep]

Code

Const ScreenOn = -1&
    Const ScreenOff = 2&
    Const SC_MONITORPOWER = &HF170&
    Const WM_SYSCOMMAND = &H112

    Declare Auto Function SendMessage Lib "user32" ( _
    ByVal hWnd As IntPtr, _
    ByVal Msg As Integer, _
    ByVal wParam As Integer, _
    ByVal lParam As Integer) As Integer

    Function SetScreen(Optional ByVal bln As Boolean = True) As Integer
        SetScreen = SendMessage(Handle, WM_SYSCOMMAND, SC_MONITORPOWER, IIf(bln, ScreenOn, ScreenOff))
    End Function

Put the above in your code then you can use this

Code

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        SetScreen(False)
    End Sub

to call the function.

[DexHacker]

You could use your code after a 4 second delay of running this code
https://hackforums.net/showthread.php?tid=422248