| | Re: BB10 Calendars have gone blank
Open your calendar and swipe downward from the top of the screen to reveal settings for the calendar. Under "Manage" make sure your calendar(s) you want displayed are checked. There is also a "Refresh" button there that will force a date exchange with your calendar.
You can try deleting the calendar account(s) and immediately re-add them. Sometimes if an online/cloud linkage breaks this will restart it.