If you, however, already checked the activation and the entries are still not visible, the problem becomes a bit more serious. At this point you need to know, if you sync your calendars/lists or if you keep them only locally.

If you sync your data, go to the online calendar and check, if you see your events there. If yes, you can relax, because you data is secured on the servers of the partner and you don't see it because of a general sync issue. The problem can be easily solved by removing and re-adding the affected account in the →  Android OS Settings →   Accounts & Sync (or similar).

If you saved your data only locally, you need your manual backup right now. The local calendars are kept only locally (as the name says) in the calendar storage on your device. They are NOT synced with any source and therefore are also NOT secured. The backup copy needs to be manually done by the user (for that reason we built in functions which allow the backup in BC 2). Should there be the smallest glitch in the calendar storage (it may be even caused by the device reboot) and you don't have backup, the non-secured data is irretrievably lost. Having a backup copy you can easily import the files in the →  BC 2 Settings →   Maintenance →   Import calendars/lists.

Please note that BC (or any other calendar app for that matter) does not actually store your calendar data. This is done in calendar storage of the device. The apps are just a managing tool, which allows you editing of their content.