You are connected through his PC? or the router is just downstairs?
There are so many factors that can effect wireless that its not funny. Even if your brother's is right beside yours a number of things could effect your signal that doesn't his.
What type of wireless "device" do you have installed? PCI? USB dongle? USB cabled?
Of the 3 I like the UCB cabled cause you can move the device around to find the best place to get a signal. My idea on wireless is get the devices as high as you can so the signal can be broadcast as wide as possible.
Now as far as while it says not connected and yet messaging works, no idea lol. Anytime I have a wireless issue I remove from Device manager, uninstall any programs and reboot. The install a fresh copy of everything.
I also stopped using the wireless software and use Windows Zero Config. to do the connecting for me.
When this happens open a command prompt and try pinging google or something. Do they go through?