Windows XP

Hi everybody!
I'm using Windows XP.My system is automatically shutdown after a few hours (even less) working. There is no virus .I've reinstalled the OS but nothing changed.Does anybody have an idea what has happened?What can i do?
Any help would be appriciated!

I guess that it may be some h/w probleme. Might check RAM and Motherbord. Also can be happen by the overheating of CPU.

Do you get any messages in the event logs around the time of shutdown? Failing these I would also lean to the overheating/hardware problem theory.

I thought about that too, sounds like its overheating. Take off your computers case and monitor the temperature.

Go to Bios Setup and check the cpu and case temp if this ok check the power voltage.If the problem was the Ram you are listening a repeated beep in the boot of the system.

I guess that it may be some h/w probleme. Might check RAM and Motherbord. Also can be happen by the overheating of CPU.

In edition to my previous suggestion another thing i would suggest that could be some virus or malware also.

Disconnect your computer from any network if it is in any network and then run a good antivirus s/w to check for virus. Also make sure that your virus s/w has latest updated virus defination set.