Thank you for your post.
When you install FileMaker Pro, the Help folder should contain the Help file named "fmpro". The full path for the file would be:
Computer -> Local Disk (C:) -> Program Files -> FileMaker -> FileMaker Pro 13 -> English Extras -> Help -> fmpro
If the file is present, double-click "fmpro", and the Help file should open. If it is also blank, then remove the Help folder and reinstall FileMaker Pro.
Keep me updated with any progress.