1- Close SQL Server Management Studio.
2- Search for the SQL Server Configuration Manager program.
3-from the options on the left choose, SQL Server Services.
4- From the services on the right check if the SQL server Agent state is running or stopped, if it is stopped, right click and click Start.
5- If you can’t click Start- then right click on SQL Server Agent (SQLEXPRESS) and then click Properties and when the Properties window opens, click Service and choose Automatic from the Start Mode drop down menu, then click Apply and OK. Now you can right-click on SQL Server Agent and Start. After the state has changed to running, open and enjoy your SQL Server Management Studio.
6- If after you have done all the above still you are having problems, try to start (change the state to running) the SQL Server (SQLEXPRESS) service.