It looks like the issue is with the connection string to the organisation database. This is stored in the Organization table in the MSCRM_Config database. It is not supported to directly edit this; the supported resolution would be to delete the organization, then import it using Deployment Manager, which will recreated the record in the Organization table
Try to check whether MS SQL server service is running by going to DB server , services.msc
In addition you can also try to check whether you are able to reach DB server from CRM front end server.
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