"iPhone won't connect to network, shows error 50?"に関する回答1. Connect your device to your computer using the cable that came with your device. You should see this message: "The software on [your device name] needs to be restored to factory settings or updated." 2. Click Update to reinstall iOS. Your personal data is preserved. Maybe this should help?
"Why can't I download and install an app?"に関する回答You can fix this by 2 steps: 1. Just search the internet for your .apk file, in your case facebook.apk. 2. Factory reset: - Just Go to settings - Phone and Storage - Factory Reset