My daughter's laptop computer, running Win XP home, shuts
down abrubtly, no error message, nothing, periodically.  
It occurs whether the system is on battery or ac power.

I have recently gone through a lengthy process of virus
removal with a helpful techie on Tech Support Guys, and
all of the virus symptoms seem to have disappeared.  
However, when I attempt to run a full system scan using
updated NAV, the system invariably shuts down before the
scan is complete.

Any hints would be appreciated, I know I haven't given
all of the technical details here but if anyone has any
ideas I will elaborate.  Thanks to anyone who may be able
to assist in advance...