[Windows Central Question]

I was surfing on facebook through my lumia. It automatically shuts down. and when I tried to power it on there's black screen with a message on top displaying : "ERROR : Unable to find a bootable option. Press any key to shut down.
I've unlocked my phone. And I'm using a Vodafone IN SIM Card on my At&t Lumia 520.
How do I fix this problem?
I'm living outside US. I've tried using NSRT but it doesn't recognizes my model and says unsupported model.
Also tried Nokia suite but it didn't helped me.
It's been a week since I've used my phone.
I'm expecting a solution in here.
Please help me out experts.

Thanks.

[RumoredNow]

Do a Hard Reset with the physical buttons on the phone: Nokia Lumia 520 hard reset

This will flash the last OS version stored in memory. You loose all data, but can get your last backup restored during setup.

​NSRT isn't seeing the device because the bootloader is corrupted.