Wireless internet help

[adhesivestp]

Alright, so ive been using a laptop upstairs with perfect internet connection for a year while my modem and wireless router is downstairs. My brother recently bought a laptop and here is where the the problems come in. His room is on opposite side of the house downstairs. Since he's gotten his laptop my wireless connection does not work while we are both at seperate ends of the house but his does (he is downstairs a room over from the router). But if he brings his computer upstairs near my laptop both of are connections work at the same time with no problems. What would cause this? What is weird is when it wont connect it still shows full bars for how strong the connection is but cannot connect to the network. Im pretty sure its the router not being strong enough but i dont get why it still would show full bars but not connect. Any suggestions?