Check SELECT @@version.

If it is SQL Server 2008, please follow below. If you have tried repairing option. Check again SELECT @@Version.

For SQL Server 2008:

Download the Service pack 3 manually and install. You can obtain it from here: http://www.microsoft.com/download/en/details.aspx?id=27594.

NOTE:

Please take in consideration SQL Server 2008 SP3 cannot be applied on a SQL Server 2008 R2 instance.

SQL Server 2008 and SQL Server 2008 R2 are two different realeases of SQL Server, and updates for one of them do not apply to the other.