Quote - the computer shuts off. It doesn't go through a shut down phase. The power light does not go off, but nothing responds and the heat sink fans stop. I have to hold down the power button to turn that off, wait a second and press it again to turn it on again.

Hatet to tell you this, but that was what was happening to my old computer in December and January.  It was overheating and finally just died. I couldn't get it to power on and stay on long enough to boot up in the end.  Plus all of the overheating ended up melting the motherboard.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi