Is it a laptop/ desktop

LAPTOP
Did you have any hardware upgrades?

DONT REMEMBER, ONCE I INCREASED MY RAM
How is your power supply? - SHOULD BE OKEY
Do you use batteries? - USUALLY POWER CORD
Do you have fluctuating voltages? - NO
Is the CPU overheating? - COULD BE
How long does the computer stay on without being shut down automatically?VARIES 1 HR TO 12 HRS
Does it shut down while specifically doing something, like reading a specific file or using an application?- NO PREFERENCES

Any messages/ warnings before being shutdown?- NOT AT ALL
.............

What is the OS you're using? Since you're using MS Word, I assume you have XP/Vista. Check your power option settings from Control panel. Check if they are all correct.

XP, HOW DO I CHECK THAT POWER OPTION

What kind of CPU do you have? Computer make and model? RAM?

ACER, INTEL PENTIUM,  1.7 GHZ, 1.24 GB RAM

Well, if you are able to use internet, go to www.pcpitstop.com to diagnose the problems with your computer. This will help you to figure out any problems with your system most of the times.

THNAKS