Restarts automatically when I try to download

I have windows xp installed on my system. It restarts automatically when I try to download something from Internet

My computer has Windows XP. It restarts automatically when I try to download anything from Internet. How can I fix the problem????

Solution:- there could be many reasons for that-

-->Overheating, if it reamains on for very very long times.
But if it happens only while using Internet, it could also be some kind of conflict also try the following, see if it helps.
-->it could be the system settings that if any windows error will come it will restart, for removing it --
Right click on My Computer, select properties, go to the tab Advanced, then under Start up and recovery go to settings.
Here under System failure unchecked the check box which says automatically restart.