Laptop freeze after 'end current session' or 'shutdown'

[Bruno Costacurta <cob1@biz.tiscali.be>]

Hello,

my laptop often freeze after end 'current session' 
or 'shutdown' operations. I'm using etch on an Acer Aspire 9100.

Difficult to give more details as nothing is displayed but computer 
is still on (ie. fan is running..etc..) and I have to remove 
alimentation (sector+battery) to switch it off. 
Even more tricky as this freeze happens not allways but around 50%.

Thanks for any clue, or ways to grab more information (dedicated log files ?) 
about what happens when related fonctions 'end current session / shutdown' 
are called.

Bye,
Bruno