I have ubuntu installed as the sole OS on a T420. Before this I had installed the #! distro (and Xubuntu before that) and wireless worked seamlessly on either. My home hotspot shows up but when I click on it tries for a while before disconnecting.
Before going into the problem further, I wanted to double check that I entered the wifi password for my home network correctly. I went to Edit Connections >> Wi-Fi Security and changed the key, but it is still not able to connect. So I think the password is definitely correct. I don't understand why it can't connect now.