Non ha palesemente senso di "Non funziona"...Dicci cosa ti succede, se ti da qualche errore, se non fa nulla, etc...

Comuqnue l'errore che hai sicuramente commesso è questo: hai copiato il codice e basta...Se non richiami la sub full screen, è logico che non accade nulla...
Basta che nel load della form richiami la full screen: call fullscreen...
Il codice completo è questo:
codice:
Public Class Form1
    Private Declare Function GetSystemMetrics Lib "user32.dll" Alias "GetSystemMetrics" (ByVal Which As Integer) As Integer
    Private Declare Function SetWindowPos Lib "user32.dll" Alias "SetWindowPos" (ByVal hWnd As IntPtr, ByVal hWndIntertAfter As IntPtr, ByVal X As Integer, ByVal Y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal uFlags As Integer) As Boolean
    Private Const SM_CXSCREEN As Integer = 0
    Private Const SM_CYSCREEN As Integer = 1
    Private Shared HWND_TOP As IntPtr = IntPtr.Zero
    Private Const SWP_SHOWWINDOW As Integer = 64

    Public ReadOnly Property ScreenX() As Integer
        Get
            Return GetSystemMetrics(SM_CXSCREEN)
        End Get
    End Property

    Public ReadOnly Property ScreenY() As Integer
        Get
            Return GetSystemMetrics(SM_CYSCREEN)
        End Get
    End Property

    Private Sub FullScreen()
        Me.WindowState = FormWindowState.Maximized
        Me.FormBorderStyle = FormBorderStyle.None
        Me.TopMost = True
        SetWindowPos(Me.Handle, HWND_TOP, 0, 0, ScreenX, ScreenY, SWP_SHOWWINDOW)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Call FullScreen()
    End Sub
End Class