Emad's Blog

One possible reason to have an error accessing a SharePoint site (page not found, 404 error) is that content database is not accessible by Pool user.

This could happen after restoring content database using SQL restore if you don’t follow the steps exactly.

In this case you will likely find in the ULS logs an error like

SqlError: ‘Cannot open database “WSS_Content_XYZ” requested by the login. The login failed.’

Quick fix: from central administration -> Manage content databases -> select the content database and check the “remove” to remove it from the farm and then add it again. when SP adds the content database back, it makes sure all required permissions are added and this could fix the problem.