Personal Experiences,Study, Learning Blog of Abu Rashid aka Harun

Good suggestion at:
http://www.computerhope.com/issues/ch000689.htm
most probably it is CPU heating related issue.

Another good suggestion at:
http://superuser.com/questions/190620/why-does-my-computer-power-off-suddenly-and-without-warning

In my computer, I could turn on after it turned off without warning using UPS, not direct line electricity. It is weird but it works. Again, on opening up the computer, the screen shows CPU temperature and when it goes around 37 or higher Celsius that may mean it is too heat and may turn off soon.