[sql] Unable to connect to SQL Express "Error: 26-Error Locating Server/Instance Specified)

In my case, I Installed SQL Express 2012 and the problem raise after I reboot my PC. I solved so:

I go to Services -> SQL Server (SQLEXPRESS) and I see that was stopped. I started and It's say an login error. In properties, Tab Log On, I change it to Local System account , then I can start the SQL service.

Then to test it, I go to SQL Server Management Studio and I connect to .\SQLEXPRESS and it works!