MS Works Calendar

I use the Calendar feature of Works 2000, but suddenly it has stopped reminding me of events. At the appropriate interval before a scheduled event a little reminder window used to open, but it doesn't do that any more.

I know this is pretty minor in the overall scheme of things, but I found it handy, and anyway I don't like having a feature that doesn't work properly.

Is there any way to persuade this little popup to popup again?