Is your equipment hooked up to a quality surge protector/battery backup? It doesn't take much of a surge or sag in power to damage delicate electronics and make them behave in strange ways as you are describing. The fact that you also have been swapping in and out a USB wireless device may have messed up Windows networking settings *not hard to do* in your tower.

Who is also your ISP and what modem/equipment did they provide for you? Is your wireless also encrypted and locked out? You may also be a victim of someone leeching your bandwith and possibly may have taken control of the first router if you did not change the default login credentials. The fact that the laptop works on various wireless signals beyond the house indicates that the problem lies somewhere there and the fustrating part is to determine what is the variable that has changed to cause this odd wireless behavior. Have you also tried hooking up your computers via standard ethernet on the routers? What if someone else brings their laptop and attempts to connect wirelessly? What happens if you take the "bad" routers and hook them up and your laptop via your neighboors internet?

In problems like this or with any IT issue for that matter, its best to start process of elimination.