function SetFullscreenMode:Boolean;
var DeviceMode : TDevMode;
begin
 with DeviceMode do begin
 dmSize:=SizeOf(DeviceMode);
 dmBitsPerPel:=16;
 dmPelsWidth:=640;
 dmPelsHeight:=480;
 dmFields:=DM_BITSPERPEL or DM_PELSWIDTH or DM_PELSHEIGHT;
 result:=False;
 if ChangeDisplaySettings(DeviceMode,CDS_TEST or CDS_FULLSCREEN) <> DISP_CHANGE_SUCCESSFUL
  then Exit;
 Result:=ChangeDisplaySettings(DeviceMode,CDS_FULLSCREEN) = DISP_CHANGE_SUCCESSFUL;
 end;
end;
procedure RestoreDefaultMode;
var T : TDevMode absolute 0;
begin
 ChangeDisplaySettings(T,CDS_FULLSCREEN);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
 if setFullScreenMode then begin
 sleep(7000);
 RestoreDefaultMode;
 end;
end;

procedure ChangeDisplayResolution(x, y: word);
var
 dm: TDEVMODE;
begin
 ZeroMemory(@dm, sizeof(TDEVMODE));
 dm.dmSize := sizeof(TDEVMODE);
 dm.dmPelsWidth := x;
 dm.dmPelsHeight := y;
 dm.dmFields := DM_PELSWIDTH or DM_PELSHEIGHT;
 ChangeDisplaySettings(dm, 0);
end;