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I'm sorry about the issue, When did this start? What is happening when you attempt to use the camera ?
Are you receiving any type of error message?
some users are reporting the same problem, Please Backup all your important data and try a hard reset by holding down the Home and Power buttons at the same time until you feel the phone vibrate and restart. If restarting hasn’t fixed it, go to : Settings > Applications > Application manager and open the Camera app. Tap Force Stop and then, in the Storage menu, select Clear Data and Clear Cache.
Hopefully that’s resolved the issue but if not press and hold the Power, Home and Volume Up buttons together until you see the Samsung logo and then release. This launches the S7’s Android system recovery mode. Tap the Volume Down button to scroll down the list of options and then select ‘Wipe Cache Partition’ by pressing the Power button. With the cache wiped, restart the phone and see if the issue has been fixed.
If the problem persists, return the phone to shop you bought it from or contact Samsung about repairs.
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Please Backup all your important data and try one of the solutions below :
Solution 1 :
Hold down the Home and Power buttons at the same time until you feel the phone vibrate and restart.
Solution 2 :
From the menu go to Settings > Applications > Application manager and open the Camera app
Tap Force Stop and then on the Storage menu select Clear Data and Clear Cache.
Solution 3 :
Solution 4 :
Solution 5 :
Additional Information : https://www.youtube.com/watch?v=wn0f-98DM0o