Your system cannot connect to SQL Server. Go to Control Panel > Administrative Tools > Services. Check if SQL Server is running.
Also are you having this problem on the same machine that SQL Server is installed, or you are connecting to SQL Server that is installed on a different machine?
Regardless, this error is no reason to be reinstalling SQL Server and it is very likely you are making the situation worse if you keep installing new instances of SQL Server!
Please have a read through this topic also, it covers most common database connection issues: