After a debugging session...

The problem seems to be with gnome (since it is not reproduced in KDE). The sympthoms are:

1) Keyboard input and operations with windows cause loss of sync in the monitor (LG 710E 1280x1024@60Hz and all other resolutions/frequencies).
2) Monitor flashes
3) Monitor blanks (gets black for about 1sec) and then comes back.
4) No input/No loss of sync.
5) In /var/log/gdm/:0.log
[casimiro@terra gdm]$ cat :0.log

This is a pre-release version of the X server from The X.Org Foundation.
It is not supported in any way.
Bugs may be filed in the bugzilla at http://bugs.freedesktop.org/.
Select the "xorg" product for bugs you find in this release.
Before reporting bugs in pre-release versions please check the
latest version in the X.Org Foundation CVS repository.
See http://wiki.x.org/wiki/CvsPage for CVS access instructions.

X Window System Version 6.99.99.904 (7.0.0 RC 4)
Release Date: 14 December 2005
X Protocol Version 11, Revision 0, Release 6.99.99.904
Build Operating System:Linux 2.6.15-1.1875a_FC5 i686
Current Operating System: Linux terra.intramundi 2.6.15-1.1875a_FC5 #1 Tue Jan 24 11:21:07 BRST 2006 i686
Build Date: 24 January 2006
        Before reporting problems, check http://wiki.x.org
        to make sure that you have the latest version.
Module Loader present
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/usr/var/log/Xorg.0.log", Time: Tue Jan 24 17:55:13 2006
(==) Using config file: "/etc/X11/xorg.conf"
dlopen: /usr/lib/xorg/modules/extensions/libglx.so: undefined symbol: noGlxExtension
(EE) Failed to load /usr/lib/xorg/modules/extensions/libglx.so
(EE) Failed to load module "glx" (loader failed, 7)
The XKEYBOARD keymap compiler (xkbcomp) reports:
> Warning:          Multiple names for keycode 134
>                   Using <KPPT>, ignoring <I06>
> Warning:          Type "ONE_LEVEL" has 1 levels, but <RALT> has 2 symbols
>                   Ignoring extra symbols
Errors from xkbcomp are not fatal to the X server


Hello,

After yesterday upgrade, X server stoped working properly. Screen keeps 
loosing sync (aparently IO from keyboard is messing server). Tried 
something like decreasing frequency/resolution. Nothing works. The 
chipset is SIS REAL256E motherboard ASUS P4S800-MX SE). Last kernel. I 
even recompiled the kernel to ensure proper modules are present.

Best regards,

Casimiro