Hmm, you got me on this one then. I cannot see a reason for it to work for you in all rooms except that one, unless there is a flaw or limitation in your laptops WiFi. If you can, I would try testing it with yours using an external WiFi connection. One that plugs into your laptop via the USB port and see if that will get you connected. I am not saying buy one.

Just see if there is someone you can borrow one from for testing purposes. If it works for you, in that room, then it is your WiFi card that is limited for some reason. Perhaps not enough signal strength in that one room for yours to work.
If another external card works for you in there, then your only options are to either use WiFi outside there (not in there) or get an...