Windows

Try disconnecting it from the network, booting it up, then seeing if it will shutdown properly. It may be getting "caught" on the network.

i don't have much better advice...if you find it works when the network is disconnected, try waiting it out...to see if it is really hung or just busy or waiting for somehting to timeout...
try another nic? try disabling programs that start up?
did this used to work?
can you see what is running at that time in task manager? anything in event viewer?

It's not clearing everything out of memory in order to perform a shutdown. Often this is a sign of beginning corruption in Windows files.

I suggest you boot to Recovery Console... and when at the DOS prompt, type:

chkdsk /r

The "/r" is repair and it should find and repair errors.

There may also be other programs that you may need to install or re-install depending on whether the computer seems to have problems with some applications during the running of them. But not knowing what you run throughout the day... the best option is to repair Windows and then watch the computer.

Check that APM is also enabled in device manager.
You may need to select view hidden devices to see it.

If that does not do it, check out the shut down trouble shooting guide posted at www.aumha.org

Chas

Could be a corrupt profile. Try renaming or deleting it