Login failed for user 'sa'. Reason: The account is disabled. SQL Server

As the error says the particular login is Disabled. Thus, we need to enable the user.

Follow these steps to enable the user.

Go to start -> programs.
Open Sql server management studio
Login to the SQL server (using windows authentication).
Expand the security tab.
Expand the Login folder.
Select the user for which you got this error. In this case 'sa'.
Right click and select properties.
Enable the user.
Save settings.