Error: This operation can be performed only on a computer that is joined to a server farm by users who have permissions in SQL Server to read from the configuration database. To connect this server to the server farm, use the SharePoint Products Configuration Wizard, located on the Start menu in Microsoft SharePoint 2010 Products.

Si al entrar en la administración central o en cualquiera de nuestros sitios SharePoint aparece el siguiente mensaje:

This operation can be performed only on a computer that is joined to a server farm by users who have permissions in SQL Server to read from the configuration database. To connect this server to the server farm, use the SharePoint Products Configuration Wizard, located on the Start menu in Microsoft SharePoint 2010 Products.

Es por que no hay conexión contra la base de datos SQL Server. Debemos comprobar que el servidor está encendido, y que el servicio de SQL Server y la instancia está arrancada, además de que se ven las máquinas (realizando un ping por ejemplo) para saber si hay conectividad.

Ir a Inicio > Ejecutar > services.msc y arrancar el servicio de «SQL Server (MSSQLSERVER)«.