Can’t open chm files or even HTML Help

When I try to open a chm file, I get “cannot open the file: mk:@MSITStore [filepath]. I have Windows XP Pro with all the Windows updates. Another XP computer here at work can open the files fine. All our HTML Help -related files, dlls, etc, are the same in version and name. I am an administrator on my machine. I have tried reinstalling the HTML Help program as well as replaced the system files and reregistered them for that program. If I try to run hh.exe, nothing happens. If I go to a Helpmenu in a program and choose a help file that’s a chm file, nothing happens. The error I get is received when I double-click the file manually in Windows Explorer.