program Project1;

uses
  Forms,
  Windows, // не забудьте эту строчку
  Unit1 in 'Unit1.pas' {Form1};

  {$R *.RES}

var
  HM: THandle;
function Check: boolean;
begin
  HM := OpenMutex(MUTEX_ALL_ACCESS, false, 'MyOwnMutex');
  Result := (HM <> 0);
  if HM = 0 then
    HM := CreateMutex(nil, false, 'MyOwnMutex');
end;

begin
  if Check then
    Exit;
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.