Switching to console freezes PC

[Vincenzo Spinoso <vincenzo.spinoso@poste.it>]

Hi all,
I've installed Debian Lenny using 2007-08-06 netinstall image and net 
installation.
After using the PC for some time, if I switch from X to console using 
the classic CTRL+ALT+F1, then the system freezes, with keyboard/mouse 
not responding, xmms audio stopped, black screen... I must turn off and 
on the PC.
The PC is a Compaq Hp NX5000, heavily used with sarge and etch/testing 
in the past, at least til April 2006, without ANY problem.
No logs seem available, because the machine seems completely stopped.
I would like to describe you this problem, just before trying a Sid 
upgrade, but I don't know how.
Any suggestions? I'll wait for a reply, if you are interested in further 
details.

The problem is still here, after:
switching from gnome to xfce
switching from gdm to xdm or kdm
switching from xserver-xorg-video-i810 to xserver-xorg-video-intel

Thanks all, best regards!
Vincenzo