What are the Wifi security problems that a normal user can experience which will make the user unable to connect to the Internet?

Some examples are: 1. a user types in an invalid username and password to access a WiFi. 2. the date/time in the computer is wrong (say, 1980) which can lead to root certificates being invalid. 3. DOS attack.

I would like to know what problems there are from the simplest to the most complicated.