Hard to tell anything if you post no details about your network archtecture.
But usually you have to have a network interface card on each PC and a means to connect the cards via cables or wirelessly---with extra hardware required if you have more than a two PC network. Its then the hardware and software set up working together that makes the network go---and various software settings can default disable a network unless they are properly set.
But it sounds like your host computer has the modem and is working---and the client computer is getting almost nothing through.
In my case I have two win XP computers with a network interface card on each connected by a crossover cable---with the hardware connections by themselves not making a network--only after I run the microsoft internet connection sharing software am I able to acheive a working network---my set up is primitive but effective---many other have routers or additional hardware.--cable type--crossover or patch-- depends on the how the network is set up.