"localhost" always points to the computer your are sitting in front of. So, you can't access any other computer by the "localhost" url.

For testing Elgg within a LAN network either install it using the IP address of the computer you are installing it to (should be a static IP) or give the server a hostname to be used as "site url". When giving a hostname to the computer you would need to add this name to the hosts file of any computer in your LAN you want to access the server from (including the server) to allow for routing hostname -> IP address.

hi still same, i put hostname uder /etc/hosts eg.

(server ip)    elgg.domain.com

Have you changed the site url in the settings of your test installation or done a re-install with the hostname as site url? It won't work if the site itself is still using "localhost" as site url because all the links will still include "localhost" as part of the url and therefore the routing from another computer will fail.