Updating the current situation:

I removed the fan and heat sink from the CPU and thoroughly cleaned the heat sink with compressed air. Reinstalled the fan and heat sink but without any additional heat transfer "paste" between the CPU and the heat sink.

The problem remains.

The computer won't tolerate any sustained room temperature above 76°F. It will slow to a crawl and stop loading any large programs. Finally, Windows will shut itself down and the blue screen with white letters will appear warning that something is amiss and Windows was shutdown because of it.

So, is my situation simply a lack of that "paste"?

Any way to monitor CPU temperature and confirm this anomaly?

TIA