When my PC is started. There's a windows xp loading. But after that, the system is reboots all the time. How i get this problem off?

My PC restarted all the time when my Mobo was broken

It also can reboot becoz the cpu overheats before xp loading,u can do when the pc starts go in bios and check cpu temp,and watch it for like 10 sec if it increases.

did u mess around with any of the system 32, WINDOWS, or Windows Registry?? cuz if it is i would recommend to reinstall OS, never happened to me before its always worth a shot if not it must be ur mobo, or HD and ya maybe ur CPU could be screwing up make sure to check the connections and ur heatsink especially

the problem is now solved. And that is: reinstall XP again.

Now because the problem is now finish, please lock this topic. Anyone mind?

So you all jumped on hardware thing :P Most likely what was going on was that he got a bsod when booting windows and a simple insert windows disk + repair option was needed