Hi Sid,
Two possibilities: System failure or overheating.
Start/run eventvwr.msc, see if there is anything in the system or
application logs that corresponds with this spontaneous reboot. You might
also disable the restart behavior under the Control Panel/System/Advanced
tab, just uncheck the option to automatically restart on system failure.
This should cause the system to produce a blue screen or stop error that can
be researched.
If the above does not apply, then you are probably overheating. Random
reboots are often a sign of over-heating, and some systems are designed to
do this to protect the components. Things you can do:
1) 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.
2) 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.
3) 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.
--
Best of Luck,
Rick Rogers, aka "Nutcase" - Microsoft MVP
Associate Expert - WindowsXP Expert Zone
Windows help -
www.rickrogers.org