How to start service on Vista

Hi,
I have a service that I'm trying to start on windows vista
using this function:

function ServiceStart(const ServiceName: string): Boolean;
var
  SCM, SCH: SC_Handle;
  P: PChar;
begin
  Result := False;
  //SCM := OpenSCManager(nil, nil, SC_MANAGER_ALL_ACCESS);
  SCM := OpenSCManager(nil, nil, SC_MANAGER_CONNECT);
  if SCM <> 0 then
  begin
    //SCH := OpenService(SCM, PChar(ServiceName), SERVICE_ALL_ACCESS);
    SCH := OpenService(SCM, PChar(ServiceName), SERVICE_START or
SERVICE_QUERY_STATUS);
    if SCH <> 0 then begin
      Result := StartService(SCH, 0, P);
      CloseServiceHandle(SCH);
    end;
    CloseServiceHandle(SCM);
  end;
end;

On windows XP it starts ok but on vista it says that it was
unable to start the service.
I'd try to modify the previliges of the OpenSCManager function
from SC_MANAGER_CONNECT to SC_MANAGER_ALL_ACCESS and the
previliges of OpenService function from SERVICE_START or
SERVICE_QUERY_STATUS
to SERVICE_ALL_ACCESS, but doesn't work.

What's wrong? How can I start a service on vista?

Thanks,
Carlos Matos