1. Do soft reset, this is done by removing the batt. of your phone whilst phone is still on.

2. Update... It maybe that your device need some update thats why your camera is failing.

4. Memory card. Check maybe your external disc is corrupted or virus that can leads to the failing of the camera.

Best advice to u is, Remove your batt. n memory card at least 4-6 minute and insert it back again, if no changes then.