Microsoft 2000 WORD illegal operations

One of my computers when you are in word, keeps giving an illegal operation. 1. I have reformatted her harddrive and reinstalled everything because she had so many bells and whistles(weather bug,etc..) 3 times and reinstalled drivers dell sent me. Then she kept getting the illegal oper. I noticed one of the files was actually a pdf file, so I installed Acrobat reader. She retyped her memo, still get illegal oper. in all office stuff and the internet,get exception error, I’ve reformatted and reinstalled everthing. I thought maybe it was a driver, since dell emailed the video, sound and network card drivers. Any suggestions…