Why my phone blackscreen after upgrade?

[Windows Central Question]

I have lumia 520, i download the app called Lumia Camera or something but it need my phone to be upgraded to Amber, then i upgrade my phone through setting key, after downloading progress finished my phone ask my permission to upgrade the phone, i accept, but after a long time my phone only showing setting icon (u know 2 gear rolling each other) but it took a long time to finish then i reset my phone, but when i switch my phone on it only showing blackscreen (at first "NOKIA" letter was showed but it turn black.

 

[Ed Boland]

Have you tried rebooting the phone? Hold down the power and volume down buttons together for about 10 seconds until the phone vibrates. Do that, then report back...