I was going to install vim on Xcode; and I saw I've gotta reset default keychains (or something like this; system language is not set to English) and I did so.
The wireless access point I connected when I reset keychain stopped working; but other aps work as usual. The system says it cannot connect to Wi-Fi network and suggests to start diagnosis.
The diagnosis didn't give me any solution and I have no idea to solve this. Other computers successfully work with that Wi-Fi though. How can I get my computer connected to Wi-Fi?