Juan and Ganesh, you both are right. But the roles are already assigned to the users.
Its not for 1 users, its for all the users.
We can activate the user menu from Easy Access Screen menu option Menu->User Menu. But this is disables in the Menu->User Menu.
Hence any user is not able to the the user menu.
There is a Profile parameter through which we can enable or disable this option. Can you please provide me the name of that parameter.