I just post this article for someone who is facing following issue. it can be easily resolved with following steps.

1) Please go to the Control Panel

2) Click on System and Security

3) Find the Administrative Tools and do click.

4) Go to Services and see your SQL services.

5) Please do Right Click on SQL Server (SQLEXPRESS) Or (MSSQLSERVER) and start the service. (You should have to change to startup to Automatic if you don’t want to do it in manually)

6) You can reconnect to the server from SQL Enterprise Manager once you have done above steps.

Hope this help. Let me know if there any issue.