How do I get my wired xbox 360 controller to sync up/work?

When I plug my wired 360 controller in, the green lights in the middle of the controller flash and keep flashing but they don't settle to the player two position (I already have one wireless controller synced up) and the player two light on the actual console doesn't light up. I don't usually use the xbox (it's my brother's), so this may be a stupid question, but can somebody please help? Thanks!
________________________________________
best modded xbox 360 controller