Note - you need to change the caption of the main form to its run time
caption *after* running this - if you are using App.PrevInst

Another method is to use the CreateMutex API

Option Explicit

Private Declare Function FindWindow _
                Lib "user32" Alias "FindWindowA" _
                (ByVal lpClassName As String, _
                 ByVal lpWindowName As String) As Long

Private Declare Function PostMessage _
                Lib "user32" Alias "PostMessageA" _
                (ByVal hwnd As Long, _
                 ByVal wMsg As Long, _
                 ByVal wParam As Long, _
                 lParam As Any) As Long

Private Declare Function ShowWindow _
                Lib "user32" _
                (ByVal hwnd As Long, _
                 ByVal nCmdShow As Long) As Long

Const SW_SHOWNORMAL = 1

Public Sub ActivateApp(Caption$, Er As Boolean)
    Dim WinWnd As Long

    Er = False
    'Search the window
    WinWnd = FindWindow(vbNullString, Caption)
    If WinWnd = 0 Then
       Er = True
       Exit Sub
    End If
    'Show the window
    ShowWindow WinWnd, SW_SHOWNORMAL
    ' ---
    On Error Resume Next
    AppActivate Caption$

End Sub

I think you mean this function. But how find out the app's ClassName or the
app's WindowName? It's for Serv-U (ftp-server), maybe that helps.