Laptop conks out and turns itself off completely

I am starting to panic. My Toshiba Satellite has began to act weirdly.
It turns itself off w/o any sign or warning right in the middle of me working
at it. Completely shut off, conk out in a second and worringly the interval is getting shorter.

My friends say they have never heard of such thing. What is happening?
Could anyone help me?

Does it still happen if you don't boot Windows but instead stay on the POST screen (press 'pause' on the keyboard) or go into the BIOS config menu and leave it there?

If not, there's hope.

Thank you for the reply. I am beginning to suspect the problem is the over heating.
My laptop could be very hot (and the ventilator very loud).

I am thinking of trying The Air Spray. I wonder if anyone tried it for this particular
problem. I will post the result.

Thank you again