Zoom related Hardware Fault?

It's not that often that a guy who once advertised himself (tongue firmly in cheek) as "the much renowned Electronic Genius" comes asking hardware help. I need your help.

The following is happening in Zoom. I can spend hours on a browser, & that's ok, but Zoom triggers misbehaviour after ~1 hour. My Samsung NP350C laptop dies instantly. That's the fault. Let me eliminate what I can.

• I don't think it's heat related, because behaviour there is an orderly shutdown, and this is disorderly - it just goes off. The one heat sensor is in the cpu.
• I don't think it's mains related. The battery is nearly useless, but it does run the box for a short while. So if it was mains related, I'd see an orange light while the battery was recharging after a poweroff. Instead, I see no light, followed by a green (= fully charged) light and I can power up again.
• For the reason just stated, I don't think it's an external power supply issue either. That power supply just provides a 19V feed. It's stepped down inside the box.
• It's unlikely to be plugs or dodgy wires. The laptop is a 17.3" thing, and I can't carry it with one hand. I use an external keyboard & mouse, and it sits motionless for the last few years.

That left me thinking maybe some internal heat-related hardware fault. I say heat-related, because if it happens, for example, after an hour on Zoom and I reconnect, I won't get another hour, but maybe just 20 minutes. Today when it went off the second time, the battery 'charged' light returned straight away, indicating a power supply interruption, I think. I don't know enough about laptop power supplies to be categorical. My guess is that it's in the stepping-down bit of the power supply (19V==> 5V, 3.3V, etc).

EDIT: This is no tragedy. It gives me an excuse to buy something decent!