I think it's simply coincidence that this happened as MCPR doesn't touch system files. It sounds very much like something was amiss to start with and this merely proved to be the catalyst. From what you say here and the other thread it sounds to me symptomatic of some deeper issues. Possibly hardware failure or some sort of infection but that's only a guess. No antivirus is proof against everything and one has to be careful.
Do you have an XP SP3 installation disk or recovery partition that can enable a repair installation to take place? That would preserve your documents etc. but would necessitate installing many Microsoft Updates again.
If not I would take the machine to a repair shop.
You can try Technical Support online chat (via Useful Links above) - they may possibly have some ideas on what's best to do next.