Hi Dale.Johnston,
Overheating would be a typical reason for this behavior. What I mean is if the notebook has a higher internal temperature and it will power off immediately to protect the hardware. So it’s normal behavior for overheating.
Overheating can have different reasons. In most cases it’s dust that is blocking the fan. This would mean you have to clean the cooling system of your notebook using compressed air spray to blow out the dust from cooling ventilators.
Usually it should help. If not I would check the display driver. What display driver and operating system you are using?
If you install non Toshiba display driver they can also cause overheating so it’s recommendable using Toshiba’s pretested drivers only.
