ASUS Transformer Pad TF300T, Android 4.2.1
In my case I suspect a hardware problem, possible bad cable connection or maybe even cold solder joint. If I press anywhere in the upper left corner of my device (near the power switch) I get the shutdown menu and after a few seconds without making any selections, the device powers off or reboots. Even attempts to press the back button to avoid the shutdown menu result in the device rebooting or shutting down. This does not happen when the device is on a flat surface and I do not press hard on the upper left corner.
If you are experiencing the same problem, don't bother trying to fix it. I have spent more than three weeks and a slew of remedies to no resolve.
Definitely going to seek an RMA and replacement.
BTW: None of the recommended fixes, solution, tip, tricks and vodoo magic has even come close to helping.