I have had a problem with help files not working on vista before. Its probably not CCleaner unless you used registry cleaner then it may have got rid of .xml as unused file extension not sure I dont use it.
I would click help and support & it would be blank or show
"Internet Explorer cannot download / from help" error message
The problem was it had deleted the
.xml file association.
It may fix it seems to be a common problem.I found this fix on the Microsoft forums that you can download the registry file to restore file association for .xml files.
http://forums.microsoft.com/MSDN/ShowPost....84&SiteID=1I also attached the file so if link gets removed. Right click registry file click merge.