Option Explicit

Private Const MAX_PATH As Long = 260&
Private Const MAX_MODULE_NAME32 As Long = 256&
Private Const TH32CS_SNAPPROCESS As Long = &H2
Private Const TH32CS_SNAPMODULE As Long = &H8
Private Const WM_SYSCOMMAND As Long = &H112
Private Const SC_CLOSE As Long = &HF060&

Private Type PROCESSENTRY32
  dwSize As Long
  cntUsage As Long
  th32ProcessID As Long
  th32DefaultHeapID As Long
  th32ModuleID As Long
  cntThreads As Long
  th32ParentProcessID As Long
  pcPriClassBase As Long
  dwFlags As Long
  szExeFile As String * MAX_PATH
End Type
   
Private Type MODULEENTRY32
  dwSize As Long
  th32ModuleID As Long
  th32ProcessID As Long
  GlblcntUsage As Long
  ProccntUsage As Long
  modBaseAddr As Long
  modBaseSize As Long
  hModule As Long
  szModule As String * MAX_MODULE_NAME32
  szExeFile As String * MAX_PATH
End Type

Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" ( _
   ByVal hWnd As Long, _
   ByVal wMsg As Long, _
   ByVal wParam As Long, _
   ByRef lParam As Any) As Long

Private Declare Function Process32First Lib "kernel32.dll" ( _
   ByVal hSnapshot As Long, _
   ByRef lppe As PROCESSENTRY32) As Long

Private Declare Function Process32Next Lib "kernel32.dll" ( _
   ByVal hSnapshot As Long, _
   ByRef lppe As PROCESSENTRY32) As Long

Private Declare Function Module32First Lib "kernel32.dll" ( _
   ByVal hSnapshot As Long, _
   ByRef lpme As MODULEENTRY32) As Long
   
Private Declare Function Module32Next Lib "kernel32.dll" ( _
   ByVal hSnapshot As Long, _
   ByRef lpme As MODULEENTRY32) As Long

Private Declare Function CloseHandle Lib "kernel32.dll" ( _
   ByVal hObject As Long) As Long

Private Declare Function CreateToolhelp32Snapshot Lib "kernel32.dll" ( _
   ByVal dwFlags As Long, _
   ByVal th32ProcessID As Long) As Long

Private Declare Function GetWindowThreadProcessId Lib "user32.dll" ( _
   ByVal hWnd As Long, _
   ByRef lpdwProcessID As Long) As Long
   
Private Declare Function EnumWindows Lib "user32.dll" ( _
   ByVal lpEnumFunc As Long, _
   ByVal lParam As Long) As Long

Private lpdwFoundProcessID As Long

Public Sub CloseExe(ByVal sExeForClosing As String)
  Dim lRetval As Long
  
'  Найти PID по экзешнику
  lpdwFoundProcessID = GetProcessID(sExeForClosing)
  
  If lpdwFoundProcessID > 0 Then _
      lRetval = EnumWindows(AddressOf EnumWindowsProc, ByVal 0&

End Sub


Private Function GetProcessID(ByVal szExeFile As String) As Long
  Dim lRetvalP As Long
  Dim lRetvalM As Long
  Dim lhSnapshotP As Long
  Dim lhSnapshotM As Long
  Dim lppe As PROCESSENTRY32
  Dim lpme As MODULEENTRY32
  Dim sExeFile As String
  
  
  lhSnapshotP = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0&
  
  If lhSnapshotP = 0 Then Exit Function
  
  
  lppe.dwSize = Len(lppe)
  
  lRetvalP = Process32First(lhSnapshotP, lppe)
  
  Do While lRetvalP
    
    
    lhSnapshotM = CreateToolhelp32Snapshot(TH32CS_SNAPMODULE, lppe.th32ProcessID)
  
    If lhSnapshotM = 0 Then Exit Function
    
    lpme.dwSize = Len(lpme)
          
    lRetvalM = Module32First(lhSnapshotM, lpme)
    
    Do While lRetvalM
    
      sExeFile = StringFromBuffer(lpme.szExeFile)
  
      If LCase(sExeFile) = LCase(szExeFile) Then
        GetProcessID = lpme.th32ProcessID
  
        GoTo ExitFunction
  
      End If
  
      lRetvalM = Module32Next(lhSnapshotM, lpme)
      
    Loop
    
    
    
    lRetvalP = Process32Next(lhSnapshotP, lppe)
    
  Loop
  
ExitFunction:
  lRetvalP = CloseHandle(lhSnapshotP)
  lRetvalM = CloseHandle(lhSnapshotM)
  
End Function


Public Function EnumWindowsProc(ByVal hWnd As Long, ByVal lParam As Long) As Long
  Dim lpdwProcessID As Long
  Dim lRetval As Long
  
  lRetval = GetWindowThreadProcessId(hWnd, lpdwProcessID)

  If lRetval > 0 Then
    If lpdwProcessID = lpdwFoundProcessID Then
      Call SendMessage(hWnd, WM_SYSCOMMAND, SC_CLOSE, ByVal 0&
      
    End If
    
  End If
  
  EnumWindowsProc = 1
  
End Function


Public Function StringFromBuffer(ByVal sBuffer As String) As String
  Dim lPos As Integer

  lPos = InStr(sBuffer, vbNullChar)
  If lPos > 0 Then
    StringFromBuffer = Left$(sBuffer, lPos - 1)
    
  Else
    StringFromBuffer = sBuffer

  End If
    Debug.Print StringFromBuffer
End Function

SaveSetting App.title, "Hfpltk", "CurInstanceID", cstr(App.hInstance)

Sub tmrTerminator_Timer()
  If CLng(GetSetting(App.title, "Hfpltk", "CurInstanceID", 0))<>App.hInstance Then
    End
  End If
End Sub

Насчет форм - если параметр Unattended Execution не установлен, то окно у проекта будет в
любом случае, так же как и App.Title

Unattended Execution

Indicates that the project is intended to run without user interaction. Unattended projects have no interface elements. Any run-time functions such as messages that normally result in user interaction are written to an event log.

Собственно, за то о чем написано в хелпе

Фокус в том что через PrevInstance я легко могу узнать запущен один такой активикс или несколько