After upgrading to Windows 10, when I try to open Outlook, i get the following message:

Cannot open your default e-mail folders.  File access is denied.  You do not have the permission required to access the file C:\Users\terry1937\Documents\Outlook Files\terry1937@ymail.com.pst.

I have since reverted back to Windows 8.1 and it still has locked me out.                                                                                    

When I open the Documents file, the size is 2.5gb and the "Read Only" box is NOT checked.  How do I get the permission to access the file?  And, if I delete the .pst file, will I be able to access old emails from my Yahoo server?  HELP

After upgrading to Windows 10, when I try to open Outlook, i get the following message:

Cannot open your default e-mail folders.  File access is denied.  You do not have the permission required to access the file C:\Users\terry1937\Documents\Outlook Files\terry1937@ymail.com.pst.

I have since reverted back to Windows 8.1 and it still has locked me out.                              

See info related to the <Permissions> error in

Outlook <Send> / <Permission> / iCloud related Errors after Windows 10 update
http://answers.microsoft.com/en-us/office/forum/office_2013_release-outlook/outlook-send-error-after-windows-10-update/c4e5a73b-4191-4d8f-bf79-e4c50c36a8db?tm=1438285150624

If that doesn't work for you - additional options included at bottom of that post