If you power off the system, there is no way to provide power to the USB ports. Power for the USB ports comes from the main power rails - which are cut off when you shutdown/power off.
Grazie mille per la risposta.
Però ho un altro pc nel quale, quando lo spengo, le porte usb rimangono alimentate. Infatti ho collegato una lampada a led che posso accendere tranquillamente anche a pc spento.
Yes, it is certainly possible, in newer PC designs, to see support for USB power in S5. In a board design as old as this, however, it is not seen very often (no one had expressed the need).
Still, since it is old enough design that we no longer have board samples to verify it with, you can check yourself if support is provided. Enter BIOS Setup and navigate to the Power scene. If support is provided, there will be an option in this scene named something like USB Power in S4/S5. If it is available, you can enable it. If it is not, you are out of luck.
Allora la terrò così
Grazie mille ancora per la gentilezza. Buon proseguimento.