Hi,
Two things:
1) Overheating
2) Hardware fault
For (1): Random reboots are often a sign of over-heating. Things you can do:
a) Open the case and make sure all fans are operating, especially the cpu
fan. While you're in there, get a can of compressed air and blow out the
dust bunnies.
b) Make sure the drive tower is well ventilated and not stuck in some
department store computer desk pc cabinet with only a little vent hole in
the back.
c) Visit a local pc shop and have them add an intake or exhaust fan. This is
not something you should do on your own unless you are familiar with the air
circulation pattern inside your machine. Adding a fan can be
counterproductive if not done correctly.
For (2): You need to know what is actually causing the problem. By default,
WinXP will reboot on system failure. You need to disable this behavior so
that you get a "stop" error (commonly known as a blue screen) that will tell
you what is wrong. Go to the Control Panel/System/Advanced tab, click on
startup and recovery settings. Disable (uncheck) the box for an automatic
restart on system failure. Next time it happens, copy down the error message
word for word before shutting off and restarting the system. Post back here
with this information. If none appears, then the more likely cause is the
overheating issue.
--
Best of Luck,
Rick Rogers, aka "Nutcase" - Microsoft MVP
Associate Expert - WindowsXP Expert Zone
Windows help -
www.rickrogers.org