Cannot connect to my local instance
Go to SQL Server Configuration Manager

Start->all program->SQL Server 2008 R2->Configuration Tools->SQL Server Configuration Manager 

Explore "SQL Server Network Configuration" and then select "Protocols For MSSQLSERVER".

Check your TCP/IP Protocols in right side pane. If it is disabled then enabled it and Restart the "Sql Server(MSSQLSERVER) service" that available in  "SQL Server 2008 R2 services pane".

You can follow the same steps to make sure for other protocols and services.