Sub Main(ByVal CmdArgs() As String)
            ...
            ' Check for previous instance of the app
            If ActivatePrevInstance() Then Exit Sub
            ...
        End Sub

    <DllImport("USER32.DLL")> _
    Function SetForegroundWindow(ByVal hWnd As IntPtr) As Integer
    End Function
    <DllImport("USER32.DLL")> _
    Function ShowWindow(ByVal hWnd As IntPtr, ByVal nCmdShow As Integer) As Boolean
    End Function

    ' <summary> Checks for previous instance of the application </summary>
    Public Function ActivatePrevInstance() As Boolean
        Dim mutexName As String = Application.ProductName & " " & Application.ProductVersion
        Dim okCreatedNew As Boolean
        g_Mutex = New System.Threading.Mutex(False, mutexName, okCreatedNew)
        If okCreatedNew Then Return False

        Dim currentProcess As Process = Process.GetCurrentProcess()
        Dim processName As String = currentProcess.MainModule.ModuleName
        processName = processName.Substring( 0 , UCase(processName).IndexOf(".EXE"))

        Dim oProcess As Process
        For Each oProcess In Process.GetProcessesByName(processName)
            If oProcess.Id <> currentProcess.Id Then ' Not current instance
                If oProcess.MainModule.FileName = currentProcess.MainModule.FileName Then ' The same .EXE
                    SetForegroundWindow(oProcess.MainWindowHandle)
                    ShowWindow(oProcess.MainWindowHandle,  4 )
                    Return True
                End If
            End If
        Next
    End Function