Reboot while trying to do updates

While trying to download updates for Tune up Utilities 2008, my computer shuts down and reboots without any error messages. It runs fine otherwise. Could it be overheating or a program designed to reboot when some suspicious activity is going on? My computer is over 4 years old. It has two fans. One is running all the time the other is not running. It is an Acer 2701 running Windows XP. I use Avast AV and ZoneAlarm Pro. Thanks!

 

If it only reboots when trying to update TuneUp Utilities, then I'd either uninstall it and re-install it using a new set-up file which you can download from them, or visit their web site and get in touch with their tech support and see what they can do for you. Here's a link to their tech support (they even have a phone number!! W O W!!)
http://www.tune-up.com/support/?article=eeeae2e206024e79a1c432c8132b186d

Good luck!