[One (M7) Q&A, Help & Troubleshooting] Danny201281:
Yeah you can go ahead and use these files. That should atleast get you back to working stock rom. full instructions below

Downloads you will need

Twrp 2.6.3.3 http://techerrata.com/file/twrp2/m7/openrecovery-twrp-2.6.3.3-m7.img < ----- Needs to be in your fastboot folder

O2 Stock Firmware https://www.androidfilehost.com/?fid=95864024717074526 < ----- Needs to be in your fastboot folder

O2 Stock Nandroid https://www.androidfilehost.com/?fid=95864024717074289 < ----- Doesn't need to be in your fastboot folder

Step 1 Prepare TWRP for the Nandroid

Flash TWRP 2.6.3.3 Recovery Download it and drop it in your fastboot folder. Flash it with fastboot.

With the phone in the bootloader connected with fastboot usb.

fastboot flash recovery name-of-recovery.img
fastboot erase cache
fastboot reboot-bootloader

Now select recovery from the bootloader menu to load TWRP recovery. Select Backup from the TWRP menu and do a backup of "boot" only. (The backup itself is not important but we need to populate the backup folders on your sdcard, thats why we do this.) Reboot the phone to Android.

Step 2 Copy and restore the rom

Unzip the O2 Stock Nandroid 6.14.206.2.zip you'll get a folder with the same name containing the backup files. Connect your phone with USB to access your Internal Storage on your pc. Copy my Nandroid to your TWRP folder it should be placed in TWRP/BACKUPS/SHxxxxxxxxx (where SHxxxxxxxx Represents your device's serial number. Put the O2 Stock Nandroid 6.14.206.2 Folder in the folder labeled with your serial number.

When its finished copying open your fastboot command window and type

adb reboot recovery

Now in TWRP recovery select "Restore" and choose the stock nandroid backup and swipe the pull bar to restore the rom to your device. When its complete in the command window type

adb reboot-bootloader

Step 3 Flash the Firmware

You Should now be in the bootloader connected with fastboot usb. In the command window type.

fastboot erase cache
fastboot oem lock
fastboot reboot-bootloader

Your device will reboot to the bootloader and should now be ***RELOCKED***

fastboot oem rebootRUU

**--- Case sensative ---^^^

Your device should boot to a black screen with a Silver HTC logo. This is RUU mode. We can now flash the firmware. In the command window type

fastboot flash zip 6.14.206.2.zip

The first flash will be short, and will appear to fail. Thats normal its just a pre update preparing the hboot for the firmware so we need to do the same command again.

fastboot flash zip 6.14.206.2.zip

The second flash will take a little longer and will flash the full firmware. The progress bar on the phone screen will not reach 100% this is normal. As long as the command window has finished its output its done. Reboot to the bootloader.

fastboot reboot-bootloader

Thats it, essentially your device is now back to matching Stock firmware and rom. Optionally you can perform a factory reset with the Stock recovery.

Step 4 Stock Factory Reset

To do this Select Recovery from the bootloader menu. The screen will go black for a while then display an image of a phone with a red exclamation mark. This is normal. Hold Volume Down and press the power button (just press power don't hold it) to reveal the Stock Recovery menu, Ignore the "Failed to mount sd card" errors that's also normal.

Select Factory reset (Delete all user data) When its complete Select Reboot System from the stock recovery menu to reboot.