• Open xampp/conf/extra/httpd-xampp.conf and look for and adding:

<LocationMatch "^/(?i:(?:xampp|licenses|phpmyadmin|webalizer|server-status|server-info))">

Order deny,allow

#Deny from all

Allow from ::1 127.0.0.0/8

Allow from ::1 xxx.xxx.x.xxx (the computer's IP address)

   ErrorDocument 403 /error/HTTP_XAMPP_FORBIDDEN.html.var</LocationMatch>

• Finally, type the IP address of the computer with xampp in the address bar.

OR
For testing purpose, you only have to turn off firewall by
/etc/init.d/iptables stop