Login Problem in Ubuntu 16.04

[motahar2]

Since yesterday night can't enter in my desktop o/s ubuntu 16.04 though I entered correct password it says "Failed to start session". When, I press Alt+Ctrl+F2 it says to login. when I enter my username & password, it says incorrect.

[RobGoss]

Hello and welcome to the forums, Not really sure why this would happen but please see the following thread here for resetting your password, https://askubuntu.com/questions/24006/how-do-i-reset-a-lost-administrative-password