Unable to open the physical file , operating system error 5. (Access is denied)

Solution:

1. Add permissions to the disk contain Data and Log files
2. Add service account to login with SA
3. Take DB offline
    Alter database DB_NAME set offline with rollback immediate
4. Bring back the DB online
    Alter database DB_NAME set online with rollback immediate

this resolves the issue, else we need to try restarting SQL Services. Worst-case we need to restore the database with latest backup.