Sorry, I got the password using windows 10 cmd "netsh wlan show profile xxxxx key=clear. But when you use the password it fails to log in with a message"Some information changed since the last time you connected. We need additional information to complete the connection" . And this situation is true for not previously connected wifi. Conversely, my room mate used my laptop once. When I used cmd command, found his password and used it successfully. That is what I mean "previously used" connection. thanks