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