Try out this…. After starting Ubuntu:
Click Applications > Accessories > Passwords and Encryption Keys, here click on the first tab (i.e. Passwords:login) , right click on the same & from the pop-up menu select “Change Password”. And choose the password for login password set to same password as user account, it never asks the pass and will unlock automatically.
Click Places > Home, to see hidden files, press CTRL + H, and locate for .gnome2 folder, here u see keyrings (a folder) and search for a file called “default.keyring”, if it is there, simply delete it.