Putnam - Welcome to the Board
First question is ....
Do you have an older computer with an AT motherboard and power supply or a more current model with an ATX motherboard and power supply. AFAIK
AT boards will not shut down automatically beyond the 'It is now safe ....' screen because the BIOS
does not support APM (Advanced Power Management).
Go to Device Manager > Computer and expand that entry by clicking on the + sign - if you have a compliant BIOS
you should see 'ACPI Uniprocessor PC'.
If you see that description look at Your computer stops responding when you try to shut down in Windows XP
from the MS
Knowledge Base. If that is of no help look here
under Powerdown Issues.
Be aware, though, that even when the computer shuts down 'automatically' and all the case lights are off the motherboard remains powered up until you turn off the mains.
On many current motherboards you are alerted to this fact by a green led on the motherboard.