Hi @ Mohamed Alshat,
Use the following to determine if you have a software or a hardware problem with the front facing camera.
First try starting the phone in [http://howtosafemode.com/1947/how-to-turn-on-safe-mode-on-htc-desire-816|safe mode] to see if the front facing camera now works.
If it does, then a downloaded app may be the cause of the problem. The trick is to find out which one. You need to uninstall each downloaded app, one by one and test the camera between each uninstall to see if it works. Once it does the last downloaded app that you uninstalled is the culprit.
''If the camera still doesn’t work in safe mode'' try the following:
Backup the phone using the phone’s backup feature.
Once the backup has been completed, perform a factory restore on the phone by using the phone’s factory restore feature.
''Be aware that a factory restore (or hard reset) will erase all your data and downloaded apps. It will restore the phone to its’ factory default condition (or last system updated condition). That’s why it’s '''important''' to '''backup''' the phone '''before''' performing a factory '''restore'''.''
Once the factory restore has been done, test the camera to see if it now works.
''If it does work'', restore the phone with the backup you made earlier, using the phone’s restore feature.
Once the phone has been restored, check that the camera still works OK. If it does then the reset has resolved the problem.
''If the camera still doesn’t work with the phone in the factory default condition'', then you have a hardware problem
Here’s a link to the [guide|61423] guide.
The replacement part is available online. Just search for ''HTC Desire 816 front facing camera part'' to get results for suppliers of the part