[HTC One M8 for Windows] TheXev:
*NOTE*

THIS GUIDE WILL NOT LET YOU FLASH AN ANDROID HTC ONE M8 TO WINDOWS. THERE IS NO KNOWN WAY OF DOING THIS AS OF ME WRITING THIS COMMENT

*/NOTE*

I decided to make this guide because many non-tech/phone people will likely be trying out Windows 10 Mobile 10536 and will run into problems if they upgrade from a previous build, or eventually want to move to a new build.

Had a failure with Windows 10 Mobile? Had a botched update of some kind? As long as you can see the HTC boot screen when you power on your phone, you should be able to reflash your phone back to Windows Phone 8.1 and start over again!

The Windows Phone recovery tool (last I was aware) does not support the Verizon version of the HTC One M8 for Windows, so this method is the ONLY method for restoring the phone back to Windows Phone 8.1.

What you will need:

ACDU (the rom update utility)

Rom for your carrier:

Verizon(rom only)

AT&T(includes ACDU)

T-Mobile(includes ACDU)

USB cable (I recommend using original HTC cable to avoid problems)

Possibly USB drivers (if you don't have them when you get to the serial=>USB step, read later)

My handy reference video that is a bit old. I recommend watching this video at least ONCE before trying anything!

If you are able to, I recommend performing a backup of your phone before doing flashing any of these roms. Also, you should probably eject your SDcard just to be on the safe side. THIS WILL FACTORY RESET YOUR PHONE.

It is my experience that a Windows 10 Mobile backup will restore on a Windows 8.1 Phone. If the phone uses any Authenticators, make sure you unattach those Authenticators from the accounts they are associated with before doing this!

Step 1

: Extract ACDU to a folder.

Step 2

: Extract your carrier's rom into the same folder as ACDU

Step 3

: Make sure phone is NOT plugged into USB and 100% fully charged! Leave your data cable unplugged at this time!

Step 4

: Shut down the phone. If the phone will not shut down because the metro screen will not appear or for for some other reason, ejecting the SIM card tray will normally force the phone to reboot. If that fails, then try holding the power button + vol down for several seconds and this will force the power off.

Step 5

: With the phone off now hold both vol buttons, and then press power to power the phone. Keep holding both volume buttons down until you see a white screen with bar codes and your IMEI and other information on. This screen should read "serial" on the bottom (*note* NEVER post a picture of this screen anywhere without blacking out the barcodes and information!).

Step 6A

: Plug in your phone to USB. If the prompt at the bottom changes from "serial" to "USB", then proceed to Step 7, otherwise check the Step 6B.

Step 6B

: If did not change to the USB prompt, open your PC's device manager and see if you have an unknown device. If you do see an unknown device: Click on the Start button, then type: "Device installation settings." Change "Never install driver software from Windows Update" to "Install driver software from Windows Update if it is not found on my computer." The HTC driver should now download and install. Once you see the "USB" prompt on your phone, you are ready to continue. Change the driver setting back to its default if you have drivers you do not want Windows Update to upgrade.

Step 7

: With the USB prompt now displayed, run "ROMUpdateUtility.exe" and select yes at the Admin privileges prompt.

Step 8

: Sit back and watch the phone flash the ROM. Once the first phase of the flashing is done, you will see the HTC logo appear, and it will disappear and appear again. The phone should now proceed to boot into Windows Phone 8.1.

As far as the Verizon version of the rom goes, this rom is the shipping rom, so you will need to install all of the updates to have the newest version of Windows Phone 8.1. I recommend installing these updates before attaching a Microsoft account to the phone and restoring a backup. I recommend factory resetting the phone after installing all updates, THEN restoring your backup from your Microsoft account.

I hope this guide will help those avoid some of the pitfalls that comes with testing Windows 10 Mobile!