You get the following error during SharePoint 2013 Products Configuration Wizard on the Specify Configuration Database Settings page:
Cannot connect to database master at sql server <Servername>. The database might not exist, or the current user does not have permission to connect to it.
Your first move should be the following: Try it again, but this time mark the time between you press Next > and when the error message pops up.
Based on this:
- if its more than a few seconds, you have network connectivity issue or SQL server configuration problem (start from no 1)
- if it pops up almost instantly, you have permission problems on the SQL server instance (See no. 10 and 9)