First, you can force the device to shut down by holding down the power button for a few seconds. If, however, you can still interact with the device, try pressing Ctrl-Shift-Esc. When the Task Manager opens, click "More details" and then click the CPU percentage on top.
I've attached a picture.
Which program appears on top when you do that? For me, as you can see, it's Omen Light Studio..
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