Since this started happening right after Windows 10 updated in July 2017, I'm guessing Windows is to blame. My Asus UL50-AG notebook (built 2008) came with Windows 7, now running 10. In Power Management, under "choose what happens when I close the lid" it is set to "Do Nothing." The power button is supposed to make the laptop Hibernate. Instead, when I close the lid or press the power button, my computer shuts down instantly-- nothing preserved to memory; everything goes dark like the power is cut off. I did replace the battery about the same time this started happening. Asus technical support couldn't provide a solution.