Camera Application Issues (Black Screen)

Ok so i have a iPhone 5S here and the screen was damaged and whilst the phone was damaged the camera application (or a third party application) wouldn't open the camera, it just displayed a black screen. So i changed the screen and the issue was still there so i changed the proximity sensor/front camera flex thinking it was damaged during the repair but the issue is still occurring. No signs of water damage and the phone gets warm quickly. Other than this the phone works fine.