Umbraco cannot start. A connection string is configured but the Umbraco cannot connect to the database

I'm using Umbraco CMS v7.4 with SQL Server 2014, the project was working fine until a few hours ago, when an error started showing up:

Umbraco cannot start. A connection string is configured but the Umbraco cannot connect to the database

The error occurs when I tried to open the website, see the image below:

I tried the following:

• Checked to see if SQL Server is running
• Checked the connection string credentials in web.config

Any help is appreciated.

After a few tries, even I loaded the backed up DB, I found that it caused by the DB login, the user in the connection string was having a password expiration enabled (the password had expired).

So, this is what I did:

• Open the SQL server
• Logged in as the user used in the connection string
• Created a new password
• Updated the web.config connection string "Password"

Hope this will help