[One (M8) Q&A, Help & Troubleshooting] ben_at_xda:
Hi.

Maybe someone of you may help me or knows someone who or a tool which might help me. Up to now I have not found a solution which would preserve the data stored on my smartphone.

Problem description:

When I start my smartphone (with German locale settings), after HTC splash screen, when lock screen or screen for PIN should appear, I can see a notification box saying ""System UI" wurde beendet" (I guess maybe something like ""System UI" was stopped" for English locale).

This notification box is in front of my clock and the lock icon. As the notification box is in front, the only option I have is to press "OK". I cannot unlock the screen or change any settings.

When I confirm with "OK", all UI elements disappear (i.e. no menu, lock icon, clock etc. any more) and screen is switching between black screen and a background picture of a landscape in a irregular interval.

Rebooting or rebooting in safe mode ("Abgesicherter Modus" in German) leads to the same result.

So currently I cannot change any settings, backup any data etc. as there is no UI.

Main problem:

I have no up-to-date backup and need to find a way to solve the issue WITHOUT DATA LOSS (or being able to do a backup before I erase/wipe any data).

"What was done before it happened the first time?" :

One week ago I was in holidays and was using my smartphone throughout the whole day taking photos, navigating etc. and at some point the battery was empty (Don't know if this has anything to do with the current). No problem, I reloaded the phone and after startup there was a notifaction box that apps have to be updated. After that phone started, I could unlock it, my start screens had been reset (i.e. my app shortcuts and widgets had disappeared) and I had to recreate app shortcuts etc., but so far the phone was working fine. When taking my flight home, I used the phone in flight mode to listen to Spotify. After landing I restarted my phone and voila, the ""System UI" wurde beendet" appeared for the first time.

Basic information about smartphone:

I am using a HTC One M8, bought in April 2015 (so at the time writing this, more than 2 years have passed).

USB debugging (adb) is not enabled, I can see the phone only when booting into FASTBOOT USB via fastboot command.

Phone is not rooted. I have no custom ROM or custom recovery installed.

The output of fastboot getvar all is following (imei and serialno XXXed-out):

fastboot getvar all
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0000
(bootloader) version-baseband: 1.29.214500021.12G
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 6.12.111.4
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: XXXXXXXXXXXX
(bootloader) imei: XXXXXXXXXXXXXXX
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B10000
(bootloader) cidnum: T-MOB101
(bootloader) battery-status: good
(bootloader) battery-voltage: 0mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: 76df2b54
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0

I have found solution proposals using factory reset etc., but all that would wipe my data as far as I understand and I need to backup my data somehow before executing such steps. But without a UI, how to perform a backup? Is there some hidden feature to enable adb from fastboot or to restore just the system UI without losing data? Any other ideas?

HTC support proposed just some steps which are based on UI (which I don't have) or resetting (which would delete data). If I would send the phone in, data would also be lost.

For data recovery they proposed the company "w-support.com"

Help or pointing to some helpful tool or person would be much appreciated!