Help for MS products in XP disappears

Several XP machines where I work lost their ability to display any help for Microsoft products. For example, trying to access help from any Office product yields a blank help box. Trying to run “Help and Support” from the Start menu, or running msinfo32.exe turns the cursor to an hourglass for a couple of seconds then does nothing. Help for non-MS products works great.

A web search turns up this problem when using a particular registry cleaner program, but that’s not the case with us. I think I’ve narrowed it down to an incompatibility with some other industry-specific softare we use, but I’d like to know if there’s any relatively easy way to fix the problem, short of an OS reinstall (repairing the installation didn’t fix it.)

Thanks!