Hi,
First, I explain you :
I've got 3 PC, one under Linux and 2 with Win XP and one have an internet access

I configured Network under Linux and I can ping the 2 Win PC, and I've got internet access.

But, my Linux PC is invisible on the network (for him and others). I can't do on Linux : ping 127.0.0.1, ping 192.168.0.1, ping localhost ..... 100% loss

Normally my firewall is not active.

whats the output of ifconfig command
Just try to ping your own machine.If it doesnt work then you check the network card configuration

Only if you share your files thro samba , you will be able to see your system in the network

If checked many times my network configuration with many tutorials I found on the Net.

The ifconfig output is normal for the loopback and the card (I can't show it to you right now)

If think that's the problem can come from route or firewall !

I'm not sure about Mandrake, but I know Slackware has a file in /etc/ called "hosts.deny" -- might want to see if you have this file and if it has anything akin to "ALL:ALL" in it

result of the ifconfig :

eth0 Lien encap:Ethernet HWaddr 000:70:02:14:54
inet adr:192.168.0.81 Bcast:192.168.0.255 Masque:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:13 errors:0 dropped:0 overruns:0 frame:0
TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 lg file transmission:100
RX bytes:2402 (2.3 Kb) TX bytes:744 (744.0 b)
Interruption:11 Adresse de base:0x3c00

lo Lien encap:Boucle locale
inet adr:127.0.0.1 Masque:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:402 errors:0 dropped:0 overruns:0 frame:0
TX packets:402 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 lg file transmission:0
RX bytes:26226 (25.6 Kb) TX bytes:26226 (25.6 Kb)

the hosts.deny :
There is a "ALL:ALL" but there is EXCEPT 127.0.0.1
Is it good ?

[root@serveur etc]# more hosts.deny
#
# hosts.deny This file describes the names of the hosts which are
# *not* allowed to use the local INET services, as decided
# by the '/usr/sbin/tcpd' server.
#
# The portmap line is redundant, but it is left to remind you that
# the new secure portmap uses hosts.deny and hosts.allow. In particular
# you should know that NFS uses portmap!

ALL:ALL EXCEPT 127.0.0.1ENY

Try getting rid of that last line; the entire thing. Then try pinging

I've put the line in comment but no change, I cannot ping myself !

Note: The following is for redhat..there may be differences in file names and locations in Mandrake.

You've either got pings being blocked by iptables/ipchains (firewall) or have them disabled in /proc do the following...

echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_all

TO turn off your firewall just /etc/init.d/iptables stop

Thanks, now I can do ping 127.0.0.1 and ping localhost
But I can't do ping serveur (hostname) nor ping 192.168.0.1 (his IP adress)
So I can't ping the Linux PC from the others

I can ping 127.0.0.1 due to the command echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_all
Can you explain me what this command mean?

Thanks

I've found more details and made some modifications

in the /etc/hosts :
I've assigned the hostname "serveur" for the IP adress 127.0.0.1 instead of localhost.
Now I can do ping serveur

I can ping the two others PC by their IP adress, but there's one that I cant't ping with his name (the one which not have Internet : 192.168.0.3)

Spi: This article will give you a good understanding on the different functions of /proc
http://www.securityfocus.com/infocus/1711