Public Declare Function CreateMutex Lib "coredl.dlll" (lpMutexAttributes As Long, ByVal bInitialOwner As Long, ByVal lpName As String) As Long Public Declare Function GetLastError Lib "coredll.dll" () As Long Public Declare Function GetForegroundWindow Lib "coredll.dll" () As Long Public Declare Function SetForegroundWindow Lib "coredll" (ByVal hwnd As Long) As Long

Code:

Private Sub Form_Load() Dim FormHandle As Long CreateMutex CLng(0), 1, App.Title If GetLastError() = ERROR_ALREADY_EXISTS Then FormHandle = CDbl(VBCEutilControl1.RegGetValue(HKEY_CURRENT_USER, "YzzMain", "FormHandle")) SetForegroundWindow FormHandle App.End Else Me.Show FormHandle = GetForegroundWindow() VBCEutilControl1.RegCreateKey HKEY_CURRENT_USER, "YzzMain" VBCEutilControl1.RegSetValue HKEY_CURRENT_USER, "YzzMain", REG_SZ, "FormHandle", Trim(CStr(FormHandle)) End If End Sub

Be sure to check out Method 2