Hello i actually know the problem you speak
of since i work for a major computer call
centre and get this issue sometimes.
Its actually being caused by
a invalid/not properly loaded device driver
or incompatable software
this behaviour only happens in windows 2000
and windows xp, as there is a option that
allows you to select reboot on system error.
In Xp if you goto system properties, advanced
tab, startup and recovery you should see a option that allows you restart computer on system
failure, and this applies to device drivers
as well not just a blue screen of death.
If you look in device manager or
event viewer of w2k/xp you should
see what is actually causing this.
If this doesn't help you it is also known
that some us robotics modems external, and internal
that the software/hardware isn't compatable
and that should also be checked.
One other device that is known to cause
this is the palm pilot attached to a serial port
i dont know if you have one, but if you do
unattach it and it probably wont restart anymore.
And a old issue with all versions of windows
is a corrupt sound file on exit will somtimes
cause windows to restart.
And the final reason as of late is the roxio/adaptec
easy cd creator is incompatable with xp all except
the most recent versions with xp, will cause
system to reboot..
So try all of these as im sure one of them
will be the answer..
Daejin.