Windows XP Shutdown issues
This may/may not apply but it's worth a shot.
when the probem starts, shut down and insert the XP CD
make sure you can boot from cd and boot into the XP install.
When you see the "HIT F5 to load 3rd party drivers" hit F4
you will eventually be given a forced computer type install list - scroll up to the top and try using the ACPI installs that apply to your system (there might be 2) - if these cause the same problem, try the standard PC setup near the bottom.
Sometimes windows cannot identify or mis-identifiess the power management.
good luck
-Streigh