Two things to try:
1. Don't login as administrator, but use "run as administrator" to run File Explorer or command. That's not the same: run-as-administrator gives you more permissions than just logging in as administrator.
2. Make a Linux disc or stick to boot from and delete it in the Linux file manager. One of the nice (albeit dangerous) things of Linux is that it doesn't look at Windows permissions.

The chance of success of #1 is greater than 0, but not 1. The chance of success of #2 is 1, in my experience.