Bad Cable? I can't figure it out

I can't figure out the problem here, so hopefully someone can help.

Here's the original set up: modem in the office which is in the back of the house. Modem connected to WAN port on Linksys router. Linksys router broadcasts wireless signal just fine and I can connect to Internet on my laptop, but I want a stronger signal.

Configuration #1:

I want the Linksys router in the kitchen. The house was built with a loose ethernet cable running through the wall from the office to the kitchen with RJ-45 on one end (office) and coupler on the other (kitchen), so I plugged in that cable to the modem and
the other end to a straight-thru cat5e which goes to the Linksys WAN and that would be the solution. Not so.

The problem: I am connected to the network on my laptop but have no internet access, as determined by the Windows 7 wireless icon with a warning exclamation point.

Configuration #2:

I tried something else: I have an old D-link router and connected a regular ethernet cable to from the modem to the WAN port of the D-Link. The cable from the office to the kitchen goes from the LAN of the D-Link to the WAN of the Linksys. Wireless internet now works on my laptop, but I get 1/3 the connection speed - Originally 15mbps now 5mbps at best using speed test.

I've checked several times and am fairly certain all ethernet cables used are straight-thru and not crossover.

Why would configuration #2 work but not configuration #1? The only difference between them is that rather than connecting the in-wall ethernet cable directly to the modem, it connects to the LAN port of a secondary router which router's WAN port connects directly to the modem.

The Linksys works fine when I connect its WAN directly to the modem with a regular ethernet cable, but I don't want to run another cable through the wall just to get it working in the kitchen.

Any ideas of why this would be happening? I appreciate the help.