I messed up installing a ROM and now I need help - Android Q&A, Help & Troubleshooting

Hello everyone,
I have a rooted, unlocked, s-on htc m8 with TWRP recovery, which I seem to have messed up pretty badly.
I was trying to follow a guide to convert my phone to GPe. Being a complete noob I stupidly overlooked the step:
"Connect your HTC One to your computer using a USB cable and copy the ROM file to your phone’s SD card root folder."
Actually I don't even know which file that would be since the zip-file I downloaded had a boot.img file but nothing with a .rom extension. Anyway I missed this step and flashed the boot.img file to my phone using fastboot
"Fastboot flash boot boot.img
fastboot reboot"
The phone got stuck in a boot loop hanging at the HTC splash. I managed to get to recovery and, after reading xda-university.com/as-a-user/how-to-recover-from-a-bootloop page I did a factory reset wiping the data cache and dalvik. Now if I try to boot it regularly it doesn't even get to the splash I just get a black screen. I can still get into the bootloader by holding power + vol up and then vol down once it reboots.
I could really use some help on this, I'm way out of my depth and the phone was a present from my gf . All I want now is to get the thing back to being a working phone.
Thanks in advance,

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phb07jm said:
Hello everyone,
I have a rooted, unlocked, s-on htc m8 with TWRP recovery, which I seem to have messed up pretty badly.
I was trying to follow a guide to convert my phone to GPe. Being a complete noob I stupidly overlooked the step:
"Connect your HTC One to your computer using a USB cable and copy the ROM file to your phone’s SD card root folder."
Actually I don't even know which file that would be since the zip-file I downloaded had a boot.img file but nothing with a .rom extension. Anyway I missed this step and flashed the boot.img file to my phone using fastboot
"Fastboot flash boot boot.img
fastboot reboot"
The phone got stuck in a boot loop hanging at the HTC splash. I managed to get to recovery and, after reading xda-university.com/as-a-user/how-to-recover-from-a-bootloop page I did a factory reset wiping the data cache and dalvik. Now if I try to boot it regularly it doesn't even get to the splash I just get a black screen. I can still get into the bootloader by holding power + vol up and then vol down once it reboots.
I could really use some help on this, I'm way out of my depth and the phone was a present from my gf . All I want now is to get the thing back to being a working phone.
Thanks in advance,
Click to expand...
Click to collapse
So you have access to fastboot? Good, run this command "fastboot getvar all", remove the serial number and imei, and post the results. Good news? Running the proper RUU will fix this and only take about 15 minutes.
---------- Post added at 10:19 PM ---------- Previous post was at 10:18 PM ----------
bford152 said:
So you have access to fastboot? Good, run this command "fastboot getvar all", remove the serial number and imei, and post the results. Good news? Running the proper RUU will fix his and only take about 15 minutes.
Click to expand...
Click to collapse
BTW, you have to be S-off to convert to GPe

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Thanks for the speedy reply!
That is good news! This is the output from getvar all:
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0
(bootloader) version-baseband: 1.24.21331
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 4.16.1540.8
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno:~~~~~~~~~~~
(bootloader) imei: ~~~~~~~~~~~
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul_ca
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B12000
(bootloader) cidnum: 11111111
(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: 3aa067d
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
finished. total time: 0.043s
Is it just a question of downloading the stock RUU (presumably from htc) and running it while connected via fastboot USB.
Thanks again,

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phb07jm said:
Thanks for the speedy reply!
That is good news! This is the output from getvar all:
(bootloader) version: 0.5
(bootloader) version-bootloader: 3.19.0.0
(bootloader) version-baseband: 1.24.21331
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 4.16.1540.8
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno:~~~~~~~~~~~
(bootloader) imei: ~~~~~~~~~~~
(bootloader) imei2: Not Support
(bootloader) meid: 00000000000000
(bootloader) product: m8_ul_ca
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B12000
(bootloader) cidnum: 11111111
(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: 3aa067d
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
finished. total time: 0.043s
Is it just a question of downloading the stock RUU (presumably from htc) and running it while connected via fastboot USB.
Thanks again,
Click to expand...
Click to collapse
Hey, just download and run this from a PC... It'll update your AT&T device (I'm assuming) to Marshmallow Unlocked/Dev Ed http://www.htc.com/us/support/htc-one-m8/news/
Edit: BTW, make sure the phone is connected to the PC in fastboot mode

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That worked perfectly!
Thanks so much for getting me out of trouble, and as a bonus updated to Marshmallow.