no command screen on my samsung galaxy a5 sm-a520f

[rogdevil]

my device was runnig good but one day it got stuck in a boot loop and now it first shows installing updates and then it shows a screen with a yellow triange with an exclamination mark written with "No command"

[TechnoGenuine]

Software is corrupted on your device. Flash Stock ROM using Odin (you can find tutorials on YouTube). There is 50% chances of recovering your data.

[Samsung_specialist]

Hi, 

We recommend you to connect the device to charger and press Volume down + Power key for 15 seconds. If the issue still exists, you may need to submit your device to one of our authorized service centers in order to better assist you using below link.
https://www.samsung.com/ae/support/service-center/