My laptop pops and shuts down? Why

os = xp-pro. MS office xp office suite. 1 gig processor 256k ram 30 gig hard drive. Only when I use MS word and while I am entering data on the right hand side of the keyboard does it happen. The laptop makes a popping noise and then shuts down. It creates a tmp document of the the file I was working on at the time of the popping noise. I cannot tell if this MS Word created problem or a short cut key combo that I don’t know about,but it has not happened while I use other programs.
I am lost. Help and Thanks.