I am using : Windows 10,sql express 2014 , the IIS is configured accroding to the video in DNN site,folders in wwwroot have permissions,
new database was created givving the IIS APPPOOL\[appName] the owner permissions,
i tried any possible combination ,means re-instaling SQLExpress,creating new db with a user and pwd even with SQLExpress it is not needed,
changing web.config , but i am getting the same error ?

Hi Omer,

1 - Make sure you are installing SQL with Mix authentication mode so you can set a password for the SA user;

2 - When running the DNN install, don't user the SQL Express version. Select the other option and ensure you added the correct db server instance name

Andy