Stacking 2 Linksys Cable/DSL Routers??

The way the computers are set up here is kind of tricky: on the third floor, there are two computers, which are both connected to a linksys router. On the first floor, is the cable modem. They are connected by an ethernet cable that is stapled to the side of the house. That's how it's been for the past few months and it's been working fine.

But now I've come home for the holidays and I want my computer to work on the internet as well. But there's a catch: my room is on the first floor (the same room that has the cable modem). So I put my computer in that room, hooked it up to another linksys router and then connected the router directly to the cable modem. And finally, I connected the line from the third floor (the one coming from the other linksys) to the "uplink" port on my linksys box on the first floor here. WHEW!

Now, (obviously) the internet works here on this computer. But why don't the computers on the third floor work??