Is your version of XP a full version or an update you installed over another version of Windows?
What software and hardware do you have installed/attached to the machine other than what it comes with? You can try uninstalling each one esp antivirus software or any other burning software besides Nero.
I would of course format and relead the OS if removing aftermarket software doesn't fix it. If reloading doesn't fix it and you have 2 sticks of RAM I would remove 1 at a time to see if it still does it. If you're using a full version of XP and it's doing it with and without the updates installed, it's time to call Sager tech support for a possible RMA.