X11 makes blakck screen

[Riccardo Mottola <riccardo.mottola%libero.it@localhost>]

Hi,

if I type startx, I just get a big black screen, no cursor no nothing.
I cannot change consoles, but the machine is not frozen, it works 
through the network and will shut down gently when the power-down button 
is pressed.

X spits this out:

narsil$ startx
xauth:  file /home/multix/.serverauth.538 does not exist


X.Org X Server 1.10.3
Release Date: 2011-07-08
X Protocol Version 11, Revision 0
Build Operating System: NetBSD/i386  -
Current Operating System: NetBSD narsil 6.1 NetBSD 6.1 (GENERIC) i386
Build Date: 01 August 2011  01:01:00AM

Current version of pixman: 0.23.2
        Before reporting problems, check http://wiki.X.Org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Wed Jul 31 22:48:03 2013
(==) Using default built-in configuration (12 lines)
mtrr set failed: Function not implemented


Top tells me that X is actually running and consuming all cpu:
  235 multix    28    0    22M 8140K RUN       46:18 99.02% 99.02% Xorg

The machine is a ThinkPad 600 running NetBSD 6.1. It has a Pentium-class 
processor.

cpu0 at mainbus0: Intel 586-class, 232MHz, id 0x581
acpi0 at mainbus0: Intel ACPICA 20110623
acpi0: X/RSDT: OemId <IBM   ,TP600   ,00000001>, AslId <    ,00000000>


Any hints or ideas? Some configuration htat has to be done? I did not 
create any xorg.conf.

Thank you,
Riccardo