Did you have them synced anywhere? Like your Samsung account or Google account? If Google, go online to Google calendar and see if they are there. If Samsung, you will have to see if they come back after syncing once your calendar app is fixed.
I would try going into Application Manager and finding the calendar app. Force Close it, then Clear cache and Clear data. Then power down phone and remove battery. Replace and boot up again. Open the calendar and go to settings and make sure it is set to sync with whatever calendars you sync with. Give it some time to sync up and check your events.