If it's S-Off that you are wanting,here's the route I took getting there with my stock T-MOBILE M8 (AtoZ from factory OEM HTC M8 stock/unrooted to Unlocked/Rooted/S-Off) :

1) BOOTLOADER UNLOCK via HTC DEV
2) Installed the proper TWRP recovery for my T-MOBILE M8, which rooted it also.
3) Ran SUNSHINE app, which gave the phone S-Off, very quick & painless/easy method of obtaining S-Off.

You may wanna wait for EarlyMon or Granite1 to chime in, as they are w/SPRINT & are well-versed in all things HTC/SPRINT.

I believe the SUNSHINE devloper highly recommends that his S-Off app works best on rooted stock ROMS.

Might wanna revert back to your stock rooted Nandroid & start from there.

 

BTW, WELCOME TO ANDROID FORUMS! arty:

Check back in to this thread & forum throughout the day & especially this evening.

The MODS that I referred to earlier should be able to get you where you need to be.

They've been an extremely valuable resource for myself & some of the nicest people you'll meet on the Internet Anywhere . :thumbup:

 

I see your M8 is listed a CDMA (dev).

Is it in fact a SPRINT M8,or,is it an unlocked,Developers Edition,or,another Carrier specific Model?

 

Is the insert coin Rom a Sense or AOSP rom?

Reason being I think you might need to flash the kernel for the Rom you are trying to flash separately.

We'll need to know what carrier you are on and your current firmware.

Boot to the Hboot screen and post up what you see there, that will give us your firmware.

I'm mobile right now, daughter's birthday, once I get to a PC, we'll be off to the races.

 

We'll try and get you on a stock Rom. Give me a minute to see if I can do this mobile. BRB.

 

Go here and download the latest stock Rom:
[SPRINT][ROM]M8WHL Stock Rooted - Base: 1.54.651.10 - theMikMik

Place the Rom on the root of your SD or internal memory .

Boot to recovery and make a nandroid backup.
Choose Wipe, and select Advanced. Check cache, Dalvik cache, data, and system. Swipe to wipe.

Go to Install, find the Rom.zip you downloaded, select it, swipe to install. Reboot

see if it works.

 

Unzip the stock rom on your pc.

Find the file - boot.img - and move it to the same folder where you have fastboot.

Get a command window in that folder, and then command -

fastboot flash boot boot.img

Once you have s-off, you'll never have to flash the boot image separately again.

 

Thanks EM, that was the next step if it didn't work.

Hopefully this will work.

 

Not to beat a dead horse,my apologies,but,just wanna clarify that we are indeed trying to restore the SPRINT HTC ONE M8 (2014).

You refer to the phone that you're having issues with as "old",which can be a relative term.

That,& you do have two phones listed,both which are labeled as HTC ONE M8's,one as a GSM Model & the other as a CDMA model,but,your carrier is T-Mobile.

THX,& again,my apologies for the horse-beating......