Try to have one modem connects to 2 separated routers!

Oxygen

Help me! I know it will works, but some how somewhere I do not do correctly.
Here is the situation:
* Comcast - our internet provider
* Motorola Modem - power line, cable line, ethernet cable connects to a 5-port ethernet switch box.
* LG router (w/only one port switch on the back, but signal very stable and strong) - power line, ethernet cable connects to the 5-port ethernet switch box.
Above setting provides wifi for everyone in the building w/o any problem, no matter up-stair or down-stair.
But the wifi signal doesn't work very well/stable in a small building right next to the main building that mention above.
So I run a very long ethernet cable through the attic from main building to small building. One end of this long ethernet cable connects to that same 5-port ethernet switch box in the main building, and another end connect to a computer in the small building. This is a wired connection setting which works fine and secure.
Now, I am trying to set up a wifi in the small building, so all other devices, like ipod touch, or other computers can be used same time in the small building.
I set up another router (D-Link) in the small building and have that long ethernet cable from the main building connects to one of LAN port on this router. I am able to see this router from my computer's network connection and it shows a very strong 5 bars signal. But this router 's "global" icon light which indicates internet connection stays on orange light (if it is connected to the internet, it will be a green light), that shows no internet connection.
Anyone know how to fix this issue?