Wonky Word Spell-check

I can't explain this well, and I don't know why it's happening, but my spell-checker in Word has gone goofy. One day it won't work, the next it will. It will stop working for a week, then mysteriously start up again. I've done virus scans. I've tried looking for working solutions online. I've tried to figure out what might be triggering it. Nothing. It's working again today, so I guess I'll just count my blessings and continue on.