Windows Authentication in SQL 2012 suddenly stopped working

Question

Hello,
I use SQL Server 2012 for a database class in college. I have been having zero problems until today, when I started up the Management Studio to work on a Project due in a week. We use Windows Authentication to just log in through our computers. Now it is
giving me an error saying the following when I try to log in with my usual credentials through Windows Authentication. 
TITLE: Connect to Server
Cannot connect to ALEC-PC.
ADDITIONAL INFORMATION:
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider:
Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 2)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=2&LinkId=20476
The system cannot find the file specified
BUTTONS:
OK
I am not trying to connect to a server, just my computer through Windows Authentication. This was not a problem until today, as I have used SQL Server on this computer before to complete previous projects. I have made no changes to my computer recently,
other than detach a database from SQL in order to send it to my professor. Then suddenly it will not connect to Database Engine, but it will connect to some of the other options under "Server Type".
Any help on this would be highly appreciated. I do apologize for not being very technical.

Answer 1

1. Make sure SQL Server Service is running
2. If a named instance, make sure SQL Server browser service is running
3. Make sure SQL Server is configured to allow remote connections
4. Examine the SQL Server error log for messages confirming that SQL is listening on the expected network interfaces and ports
5. Test server connectivity with PING from the client machine
6. Test port connectivity using TELNET or PowerShell to the server and port (from step 4) from the client machine.  For example
a. TELNET <server-name> 1433
b. PowerShell: 1433 | % { echo ((new-object Net.Sockets.TcpClient).Connect("YourServerName",$_)) "server listening on TCP port $_" }
7. Check firewall settings if step 5 or 6 connectivity test fails
Best Regards,Uri Dimant SQL Server MVP,
http://sqlblog.com/blogs/uri_dimant/
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