I am running the 64 bit version of Windows 7 and have downloaded the CHM help file from the SDL Web site. The CHM help pages show a blank display in the right pane of the help viewer. The navigation structure at the left seems to be functional and correct. Here's a screen shot of the apparently broken help page:
||This is a problem of some versions of Windows, and not a problem of the SDL help pages. See the following Microsoft Technet article for details.
Newer versions of Windows prevent chm files from displaying correctly if the chm file has been downloaded from the Internet or is stored on a network drive. In order to solve this you should copy the chm file to a local drive, right click the file name of the local copy (using Windows explorer) and click the "Unblock" button: