Please Help--Linksys Problem

I bought a linksys router and hooked it up to the cable modem. I have a main computer that is also directly hooked up to the cable modem and because it doesn't have an ethernet card, I can't use the router with it. I have another computer upstairs that I want to hook up to the cable connection through the router. I installed everything and the adapter upstairs says I have a connection--I have the little tray icon that shows the connection and everything...BUT I CAN'T DO ANYTHING. I can't open a web page, I can't go on aim...it says there's a connection but apparently none of my other programs detect it--I have no idea what's going on or how to fix it and I bought all this **** and now it doesn't even work. Can someone please help me out here?

 

You'll need to hook both PCs to the switch side of the router switch and hook it to the cable modem. Otherwise it just ain't gonna work and you won't be able to network the PCs together or have both on the internet at the same time.