Olá, Vaca.

 

Coloque este código num módulo, ele faz isso que você quer.

 

Public Const GW_HWNDPREV = 3
Declare Function OpenIcon Lib "user32" (ByVal hwnd As Long) As Long
Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Declare Function GetWindow Lib "user32" (ByVal hwnd As Long, ByVal wCmd As Long) As Long
Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As Long) As Long
Public sTrab As String * 255
Public Declare Function GetUserName Lib "advapi32.dll" _
Alias "GetUserNameA" (ByVal lpBuffer As String, nSize As Long) As Long
Public Declare Function GetComputerName Lib "kernel32" _
Alias "GetComputerNameA" (ByVal lpBuffer As String, nSize As Long) As Long

Sub Main()

    If App.PrevInstance Then
        ActivatePrevInstance
    Else
        Load frmFORMULARIO
    End If

End Sub

Sub ActivatePrevInstance()

   Dim OldTitle As String
   Dim PrevHndl As Long
   Dim result As Long

   OldTitle = App.Title

   App.Title = "Programa em execução"

   PrevHndl = FindWindow("ThunderRTMain", OldTitle)

   If PrevHndl = 0 Then
      PrevHndl = FindWindow("ThunderRT5Main", OldTitle)
   End If

   If PrevHndl = 0 Then
        PrevHndl = FindWindow("ThunderRT6Main", OldTitle)
   End If
  
   If PrevHndl = 0 Then
      Exit Sub
   End If

   PrevHndl = GetWindow(PrevHndl, GW_HWNDPREV)

   result = OpenIcon(PrevHndl)

   result = SetForegroundWindow(PrevHndl)

   End
  
End Sub

É bem provável que isto lhe sirva.

 

Rogério.