Yesterday I solved notebook with auto shutoff problem. It is a Acer. I believed it is a heat problem. So, I disassemble the unit and found out that the base of the heatsink screw has broken. It is loose from the mainboard.
I place the had modified the screw base, and screwed back the heatsink. I tested the notebook and it work perfectly event after 24 hours of burn-in test.
It save the notebook owner a lot of money (if I didnot modified the base, he may be need to change the mobo).
Next time if I encounter the same problem, I will take some photos.