Internet sharing problems

Hello,
I have adsl broadband modem with three computers. My problem is when I connect the modem directly to one computer it works fine. But, when I tried to connect it with the switch there is no light at all & it doesn't work. I tried to connect with cross over cable there is light but I can't access the internet through the modem. My question is how can I share the internet between the three computers using the adsl modem? Expecting your quick reply.

Thank you,