Unknown Virus? Keeps me out of Registry.

This XP Home ED. machine will not let me run any executables. I cannot install software, etc. I cannot run regedit nor other commands from Run. I have also tried to upgrade to Pro, but it comes up with errors due to not being able to load product catalogs, a “fatal error”. The setup log states that “Setup had problems registering the following OLEcontrol DLL: c:\windows\system32\initpki.dll. The machine had a virus program called Armor Shield recently provided by Road Runner free for one year. I could not determine if it had been updated at any time. Also, the set up screen splashes by too fast to get into it. Any ideas.