[One (M8) Q&A, Help & Troubleshooting] Swazi Samurai:
Let me start by saying this forum has provided me with a ton of support in the past. There is so much information available here that I rarely have to start my own thread. Unfortunately, I have spent the past 18 hours looking for a solution to my current problem and have come up empty handed. I'm hoping some of you are savvy enough to help me out. I will try to provide as much information as possible to help diagnose the issue.

Device

HTC One M8

Carrier: AT&T

CID: CWS_001

Unlocked HTC Bootloader

S-On

I was previously running the stock ROM rooted (based on the above) simply to disable the AT&T bloatware. As of last week, AT&T began pushing the 4.4.4 update and I made the mistake of trying to install it not realizing my custom recovery (TWRP 2.7.1.0) would prevent it. Ever since this occurred, my phone has been doing strange things, i.e. random reboots and the "AT&T" logo in the upper left corner of the task bar would flash and disappear. It eventually got to the point where my phone was stuck in a constant boot loop and the only thing that would fix it was a factory reset from TWRP recovery. The phone would then act normal for about 24 hours and then the boot loop would start again.

I decided to try solving the issue by installing the GPE 4.4.3 ROM. I performed a complete wipe in TWRP (including system) and installed the GPE ROM via ADB/Fastboot. Everything was fine from this point and all apps/data synced after I logged into my Google account. Shortly after the phone booted, I was asked to install the GPE 4.4.4 update. It was at this point that I decided to load the stock recovery image so I could simply install the OTA update. Once again, no problems. Stock recovery flashed fine and I downloaded the 4.4.4 OTA update and rebooted the phone. The phone appeared to finish the install, but failed to boot. Now I cannot get past the HTC splash screen and I do not have a custom recovery.

The factory reset option from stock recovery does not help (still gets stuck at the splash screen) and for some reason my device is no longer recognized in Fastboot which prevents me from flashing a custom recovery. I thought it may have been a driver issue so I uninstalled and reinstalled HTC Sync Manager. I also tried manually uninstalling the drivers from the USB Root Hub, pulled the battery on my laptop, and allowed Windows 7 to auto update the drivers automatically. In each case, the drivers were successfully installed, but the phone is still not recognized in Fastboot (no devices listed). I even did a system restore on my laptop to a few days before the issue and the phone still isn't recognized by HTC Sync Manager or Fastboot.

The stock recovery bootloader displays the following information:

*** TAMPERED ***

*** UNLOCKED ***

M8_UL_CA PVT SHIP S-ON

HBOOT-3.18.0.0000

RADIO-INVALID_VER_INFO

OpenDSP-INVALID_VER_INFO

OS- (2.12..1700.1)

eMMC-boot 2048MB

Based on all of this, do I have any options or is my phone bricked?

1. Is there anything I can do so my device is recognized by ADB/Fastboot so I can flash a custom recovery?

2. Can I install a ROM from the SD card with the stock recovery? I currently have the GPE 4.4.3 ROM on my SD card, but the zip is not recognized by the stock recovery. Can I rename it to something else so it can be recognized and installed?

3. Because the phone is not recognized by Windows, I cannot use the RUU method. Are there any other ways to return my phone to stock without RUU?

Any help is greatly appreciated.