HTC One stuck in white starting screen

Hi!

My brother tried to update the latest update for his HTC One and at some point it restarted and is now stuck in the white starting screen.

It's stock, I just unlocked the bootloader, but apart from that I would like to not root the phone.

I tried several things - I can get into the bootloader and also into fastboot, I did a factory reset and wiped the cache, nothing helped.
For some reason I can't do some things through fastboot, if I try for example to do "fastboot continue" I get "resuming boot... FAILED (remote: not allowed)".

Here is the bootloader information:
(bootloader) version: 0.5
(bootloader) version-bootloader: 1.54.0000
(bootloader) version-baseband: 4A.17.3250.14
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 2.24.206.7
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno: XXXXXXXXXX
(bootloader) imei: XXXXXXXXX
(bootloader) meid: 00000000000000
(bootloader) product: m7_ul
(bootloader) platform: HBOOT-8064
(bootloader) modelid: PN0710000
(bootloader) cidnum: O2___102
(bootloader) battery-status: good
(bootloader) battery-voltage: 4285mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: dirty-d959c75800
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0

Also, I'm using Mac.

If you need anymore information led me know and I will try to provide them.

Can anyone help?