Thank You, Problem Solved
Thank Dear,
I have tried and succefully Locked My WorkStation
Public Class Form1
Inherits System.Windows.Forms.Form
Private Declare Function LockWorkStation Lib "user32.dll" () As IntPtr
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
LockWorkStation()
End Sub
End Class