All was working well before but I don't understand what happened suddenly.Pleasse help.

First you must determine is software or hardware the problem.
Can you boot into another operating system and verify that the keyboard (hardware)is not broken or swap the keyboard with another one.

If you narrow it down to software on slitaz-2.0 did you install xorg ?

Yes, my key board is working and xorg also is installed.
I boot slitaz from USB also and checkde it is working in that.

Thanks.
AMD

Boot into problem slitaz with bootcode screen=text mode to see if keyboard malfunctions.
When I do this in slitaz-3.0 hwconf.sh removes slim, after your test add slim back to /etc/rcS.conf RUN_DAEMONS= after dbus and hald
If keyboard work's in text mode it may be xorg problem so configure /etc/slim.conf to boot into xvesa instead to test.

Yes, keyboard works in text mode. Some keys don't work like "home,end up down arrows pageup etc"

My computer already has arguments like the following in slim.conf

# /etc/slim.conf: Slim login manger configuration file
#

# Path, X server and arguments (if needed)
# Note: -xauth $authfile is automatically appended
default_path ./:/bin:/usr/bin:/usr/local/bin
default_xserver /usr/bin/Xvesa
xserver_arguments -ac -shadow dpms +extension Composite -screen 1024x768x24

# Commands for halt, login, etc.
halt_cmd /sbin/poweroff
reboot_cmd /sbin/reboot
console_cmd /usr/bin/xterm -C -fg white -bg black +sb -T "Console login" -e /bin/sh -l -c "exec /bin/login"
#suspend_cmd /usr/sbin/suspend

# Full path to the xauth binary
xauth_path /usr/bin/xauth

# Xauth file for server
authfile /var/run/slim.auth

# Activate numlock when slim starts. Valid values: on|off
# numlock on

# Hide the mouse cursor (note: does not work with some WMs).
# Valid values: true|false
hidecursor true

# This command is executed after a succesful login.
# you can place the %session and %theme variables
# to handle launching of specific commands in .xinitrc
# depending of chosen session and slim theme
login_cmd exec /bin/sh -l ~/.xinitrc %session

# Commands executed when starting and exiting a session.
# They can be used for registering a X11 session with
# sessreg. You can use the %user variable
#
# sessionstart_cmd some command
# sessionstop_cmd some command

# Start in daemon mode. Valid values: yes | no
# Note that this can overridden by the command line
# option "-d"
#daemon yes

# Available sessions (first one is the default).
# The current chosen session name is replaced in the login_cmd
# above, so your login command can handle different sessions.
# see the xinitrc.sample file shipped with slim sources
sessions openbox,e17,jwm

# Executed when pressing F11 (requires imagemagick)
#screenshot_cmd mtpaint -s /root/slim-shot.png

# welcome message. Available variables: %host, %domain
welcome_msg Welcome to %host

# shutdown / reboot messages
shutdown_msg The system is going down...
reboot_msg The system is rebooting...

# default user, leave blank or remove this line
# for avoid pre-loading the username.
default_user tux

# current theme, use comma separated list to specify a set to
# randomly choose from
current_theme slitaz

# Lock file
lockfile /var/lock/slim.lock

# Log file
logfile /var/log/slim.log

# Auto login default user
auto_login no


what is to be done? I tried reinstalling xorg but doesn't help.
Thank you

You have no entry to start Xorg:
# Path, X server and arguments (if needed)
# Note: -xauth $authfile is automatically appended
default_path ./:/bin:/usr/bin:/usr/local/bin
default_xserver /usr/bin/Xvesa
xserver_arguments -ac -shadow dpms +extension Composite -screen 1024x768x24

Slim is starting Xvesa

To start Xorg add whats in bold and put # in front of whats underlined:
# Path, X server and arguments (if needed)
# Note: -xauth $authfile is automatically appended
default_path ./:/bin:/usr/bin:/usr/local/bin
default_xserver /usr/bin/Xorg
#default_xserver /usr/bin/Xvesa
#xserver_arguments -ac -shadow dpms +extension Composite -screen 1024x768x24

Hello mojo,
Yes I got the arrow keys working . Thank you.

But , there is another problem which has come up.

I need to press auto-adjust screen everytime I start my computer else the resolution is not proper. I adjusted screen resolution from menu but the problem persists.Where do I make the setting ?
Thank you.

Follow this guide:
http://doc.slitaz.org/en:guides:xorg-xvesa
Configuring X
Adding Resolutions
3. Add an extra Mode to the line in the Display sub-section