i saw this once and it was a font problem -- some were corrupted.
my clue -- when word started up, it shows status in the splash window. it paused at "loading fonts" or similar language. have a look at the splash screen and it might give you a clue.
In another situation, especially Word, it would start up and run for approximately 20 seconds and then quit. I found that the problem was corrupt preference files. Go into the /Library/Preferences on your root folder and delete them. All happy.