My faithful MCAD14 no longer inserts functions. Insert|function does not open the function menu. Old MCAD files are also broken.
All of a sudden (yesterday it still worked and now it doesn't anymore) or did you not use it recently and it may have happened somewhere in the course of time?
What's your Operating System? Was it recently updated?
Can you still use it as a simple calculator?
What if you type a function's name? Try sin(1)=