Airport does not detect wireless network; it says problem = [network]"connection timeout"

It is not a problem of signal strength, and my Airport detects other networks. It used to detect the network I want to connect to, for two years. It suddenly stopped detecting the network (which is WPA Personal password-protected). When I select choose other network and type in the password, it won't connect to it claiming "connection timeout."

This happened before. Then after several days, Airport was able to detect and connect to the network I want. Now it again won't detect the network, and this seems permanent short of taking measures to address the problem. Should I try connecting manually to the network, and hodo I got about that? Thank you to anyone out there ho might be able to help.