When an account is disable it cannot be used to login to SQL Server. You will receive below error when logging-in to SQL Server using a disabled Login account:

You can enable a disabled SQL Server Login using SQL Server Management Studio or via T-SQL code.

To enable a Login using SQL Server Management Studio:

1. Open SQL Server Management Studio

2. Login to Server using a system/security administrator account

3. Locate the disabled login under Security > Logins in Object Explorer

4. Right Click on Login Name and select Properties.

5. Go to Status Tab and Select "Enabled" under "Login:"

6. Click on "OK" to apply changes.

To enable a Login using T-SQL Code:

1. Login to Management Studio with a system/security administrator account and execute below T-SQL code:

ALTER LOGIN [User01] ENABLE

GO

Executing above code will enable a disabled login account.

Hope This Helps!

Vishal

If you like this post, do like my Facebook Page -> SqlAndMe
EMail me your questions -> Vishal@SqlAndMe.com
Follow me on Twitter -> @SqlAndMe

Filed under: Management Studio, SQLServer, SQLServer 2005, SQLServer 2008, SQLServer 2008 R2, SQLServer 2012