have a sify ethernet broadband connection

hi, this is biswajit from kolkata, i have a sify ethernet broadband connection and it has a commercial plan for that i can use 256kbps speed with internet shareing options,
i am having five computers, one of them has two lan cards. one for local ethernet sify internet donnection and another for home nerwork. whenever i loged on to sify, my home network going down, so no computer in my lab can found others even printer also but when i loged off sify the home network returned and all process doing fine.
sify network address- ip- 10.23.18.10
getway- 10.23.18.1
subnetmask-255.255.255.0
dns-202.144.13.50 and 202.144.96.4
and my home network is main server(another lan card ip-192.168.0.1 subnet-255.255.255.0 and so on)
please help me out what i have to do to solve the problem.
regards
biswajit das
ph-9339736226
thanking you
biswajit