Cannot connect to the configuration database

My Issue:

 Cannot connect to the configuration database

1. SQL services is in start state, but Restarted the SQL services

2. Checked AppPool in IIS and restarted all the web sites and AppPools are looking good. But still got same error. 

3. Checked the Event viewer it shows the below error.

Cannot connect to SQL Server. machine name not found. Additional error information from SQL Server is included below.Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.

4. Tried to Login SQL using Windows authentication login failed and got response  "Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding."

5. But SA account Login successfully.

Solution:

Checked DC it was shutdown. Switched on the DC and everything back normal