I started by downloading marscore.dll from www.DLL-files.com and per their instructions for Windows XP installed it to C:\Windows\System32. It is now back with its little friends. Nevertheless, The same error message results when clicking Help&Support.
Next, a websearch located several computer forum dialogues on the identical problem. The advice included running SFC/ scannow which I did to no discerable effect and to go to C:\Windows\inf and right click "install" for pchealth.inf. Like others, doing this resulted in another error message: The file "dataspec.xml" of Windows Home Edition SP2 CD is needed.
Thats where things dead-end since, as in my case, the forum participants have systems that were factory preloaded and their warranties expired.
I was resigned to living with the bad news until I replace this computer. But on the "nothing to lose" theory I downloaded a freeware named PCInspector, a file recovery program. It immediately located dataspec.xml as a deleted but intact file and enabled me to save it to a floppy disk. Running the floppy clearly displays the file.
Finally, here's my question. Can I get dataspec.xml from Drive A to where it belongs, and if so, is that in pchealth.inf or some other path? This is pretty deep water for me and some expert advice would be appreciated.