Thanks to a security feature introduced by Microsoft after Windows XP, HTML help files downloaded from the internet are blocked. The effect is that the right hand pane of the HTML help file is blank. To unblock the file do this:

1. Extract the .chm file from the zip folder.
2. Right click on the file and select Properties
3. In the properties dialogue click the [Unblock] button or un-check the [Unblock] check box and Apply.

The .chm file will now open normally when double clicked. If you want to read the Microsoft explanation follow the link below.

https://support.microsoft.com/