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

1) Open SQL Server Management Studio and Login
2) In Object Explorer, click Security followed by Logins
3) Right click sa user and select Properties.
4) Uncheck Enforce password policy
5) Select Status. Click the Grant and Enabled radio buttons. Click OK
6) In the Registered Servers top pane, right click on the database and choose restart