Cannot Shut Down T23 after fresh install XP-Pro (solved)

[RealBlackStuff]

This is the weirdest problem I have yet seen.
Got a 'new' used T23 for a friend, installed XP-Pro from absolute scratch incl. partitioning and full format in NTFS, installed AVG and Kerio, did all the IBM-updates, M$-updates, installed Firefox and Thunderbird and then wanted to turn the laptop off. NO WAY.
Ctrl-Alt-Del does not show 'Shut Down', Start/Shut Down does not work, press Power button does not switch it off.
It will only go into hibernation at the moment.
Power settings are standard.
Where do I have to start looking?

I answered a similar problem recently in this post: http://forum.thinkpads.com/viewtopic.php?t=41516
(make a change in the User Accounts logon/logoff method), but that only brings back the Shut Down option.
It still won't shut down!
No error messages, nothing happens!

EDIT: Holding my finger on the Power button for nearly a minute (!) finally brought the laptop to its knees.
It now works fine in all aspects.
Thanks for looking anyway.