Bienvenue, Willkommen and Benvenuto, sorry that Greek is well, all Greek to me Souamitos
Do you get any kind of error message when it reboots or does it just reboot without any message ?
If it just reboots there is a setting that you can disable as XP wants to reboot at the slightest error that it detects, usually when it wouldnt cause a problem with anything.
I have attached a screenshot of the windows that you will see.
If you Right Click on My Computer, then Properties, then Advanced, then Settings in the Start Up and Recovery it will bring another box up.
In that box go to the central section, System Failure and untick the box for Automaticaly Restart.
That should solve your problem, my last installation of XP used to reboot itself randomly quite often until I unticked that box.
I had forgotten about it until you mentioned it in your last post, mine must have been ok as it was ticked on this latest installation but I have unticked mine now
I hope that this cures your problem