Keyboard not enabled at login screen

I an using an Asus EEPC 1015PEM running Natty for some months. Everything was OK until a few days ago. Now the keyboard is not enabled at the login screen. I can use the touchpad and its mouse keys to select myself from the list of users, but I cannot type my password. Only the Esc key seems to be working. Pressing other keys gives nothing.

The same situation is found with a USB keyboard plugged in and with the on-screen keyboard enabled.

The physical keyboard is OK. It has been tested at the GRUB boot screen, in Windows 7, using a live 11.04 on a USB stick (which has a login screen) and in Recovery Mode, which is being used now to create this bug report (via netroot > su tony > strartx > terminal > ubuntu-bug gdm).

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: gdm 2.32.1-0ubuntu3.2
ProcVersionSignature: Ubuntu 2.6.38-11.50-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic i686
NonfreeKernelModules: wl
Architecture: i386
Date: Fri Oct 7 11:53:52 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
ProcEnviron:
 LANGUAGE=en_GB:en
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: gdm
UpgradeStatus: No upgrade log present (probably fresh install)