Okay, consider this as a personal journal entry for quick access ;). I don’t remember the exact source, regardless I copied and kept it for years and hopefully it would help you also.

If one of your experiments goes truly bad, messing the NTFS permissions, use the following command(s) to reset them. Open an elevated command prompt and

To reset permissions for a file: icacls "full path to your file" /reset.
To reset permissions for a folder: icacls "full path to the folder" /reset.
To reset permissions for a folder, its files, and subfolders: icacls "full path to the folder" /reset /t /c /l.

Cheers.