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procedure TForm1.Button1Click(Sender: TObject); 
begin 
  SendMessage(Handle, WM_SYSCOMMAND, SC_SCREENSAVE, 1); 
end;                    

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var
  _SetSuspendState: function (Hibernate, ForceCritical, DisableWakeEvent: BOOL): BOOL
  stdcall = nil;

  function LinkAPI(const module, functionname: string): Pointer; forward;

function SetSuspendState(Hibernate, ForceCritical,
  DisableWakeEvent: Boolean): Boolean;
begin
  if not Assigned(_SetSuspendState) then
    @_SetSuspendState := LinkAPI('POWRPROF.dll', 'SetSuspendState');
  if Assigned(_SetSuspendState) then
    Result := _SetSuspendState(Hibernate, ForceCritical,
      DisableWakeEvent)
  else
    Result := False;
end;

function LinkAPI(const module, functionname: string): Pointer;
var
  hLib: HMODULE;
begin
  hLib := GetModulehandle(PChar(module));
  if hLib = 0 then
    hLib := LoadLibrary(PChar(module));
  if hLib <> 0 then
    Result := getProcAddress(hLib, PChar(functionname))
  else
    Result := nil;
end;

// Beispielaufruf:

procedure TForm1.Button1Click(Sender: TObject);
begin
  SetSuspendState(True, False, False);
end;