[Nexus 5 Q&A, Help & Troubleshooting] B:
First, here are some details of my Nexus 5:

32GB Black. D821 International Model

I'm currently living in Malaysia. My relative bought the device from Google Play Australia and brought it over to me

early adopter - I got the first hardware batch.

stock, unrooted, locked bootloader

no modifications except for

1. installing USB OTG helper apps (which seemed to harmlessly change my file directories a little (?))

a) USB Stick Plugin-TC

b) Total Commander

2. installing AOSP Kit Kat launcher ported from Nexus 4

I have actually refrained for quite some time from posting this issue which I found has been pointed out several places in the forums. But I'm at a loss. I have checked many of the threads and posts using the search function but I can't seem to find a definite answer to my unique problem.

My problem:

My Nexus 5 just died on me. It suddenly reboots in my pocket and entered into a boot loop. It continuously showed the Google screen and blacked out again. Occasionally it showed the boot animation for a while but blacked out again. And if I left it alone without attempting to turn it on, it will suddenly reboot normally to my lock screen and my homescreen (as if nothing happened), but the screen will turn black sooner or later and it's back in a boot loop again.

I can't even enter recovery mode normally because when I enter fastboot mode (this fails several times too), the screen will go black before I can select recovery mode with the volume keys. The bootloop cycle is too quick and fast-paced for me to even do anything. It's an endless frustrating cycle.

This is the second time it has happened. The first time, however, it came back from the dead as mysteriously as it died. I hurriedly factory reset and wiped dalvik-cache and cache. It stayed working for more than a week. I thought the problem has gone away. It did not, unfortunately, and I should have done more such as unlocking the bootloader, flashing factory images, etc. But I didn't and now I'm in a fix. This time (the 2nd time) it just stayed non-functional. I'm not even sure whether it's a software or a hardware problem. :(

There's also the issue of which methods to choose to solve the problem. I need help to choose which one.

Method 1:

Solve it yourself (software fix) perhaps by flashing the device's factory images through help from XDA Developers Forum. But I need to find a way to go around the issue that I can't enter fastboot or recovery. My warranty may also be affected, which may affect Method 2 mentioned below.

Method 2:

Request Google and/or LG for a replacement (hardware fix). Problem is, I'm over the return period (15 days) and I'm currently in Malaysia. It's going to be a hassle to go through my relative again for shipping and handling. I am also not familiar with the procedure.

I'm new to rooting and hacking, and it's the first time since I got a device from overseas. I don't know what to do.

Any help and advice will be very much appreciated. :)

UPDATE: the phone came back from the dead again as mysteriously as it died. And curiously at exactly 50% battery. With all my data intact, as if nothing happened. I think it's a hardware problem and will probably be requesting a replacement from Google/LG (Method 2)