Computer Turns Off By Itself

Hi,

I bought my Inspiron computer this past September and it has been working fine for the past few months.  However, just recently my computer likes to shut off by itself without me telling it to do so and with no prior warning.  And this is very frustrating, expescially when I'm typing a doucment, and out of nowhere it just suddenly shuts off on me.  I don't know what is happening and would like some advice on this.  Is my computer too hot? But sometimes I just turned it on for half an hour and it already turns off by itself.  I have left my computer on for hours before and nothing seems to happen to it. I didn't tell it to shut down, and my energy setting does not tell the computer to shut off automatically.  I'm certainly not idling for too long since I'm working on stuff.  Could it be due to viruses, worms or bugs?  My virus software is certainly not detecting anything though.  Please help!  And thanks in advance!

Sincerely,

PPSS