I think you are right about some system problem. It's an old installation.
Anyway I've done something else.
1) About Antivirus. I'm not sure Comodo is completely disabled when I close it. That's because Windows Security Center doesn't show a warning message, and continue to show the system as "protected", even when I close all the related tasks (Geekbuddy, Dragon, etc.). Anyway I can't unistall Comodo for a complete test, right now.
2) No networked drive in use.
3) About Drivers. I've found 2 drivers not working: "Microsoft ISATAP Adapter" and "6TO4 Adapter". Update of the drivers doesn't fix the warning in the hardware monitor. I'll try something later.
4) About PATH. I've found some unused path related to Jahshaka, an old video editor open source (now the project seems again active). I've cancelled the unused paths using "RapidEnvironment Editor". But this doesn't solve.
Thanks a lot for your suggestions. I'll try something in the next days.
Right now the most important thing is I can use Calibre. A New installation of the system will come soon and I think it will be the solution.
See you : )