I don't have a working ROM on my Sprint HTC One. I made an error when flashing; I'm on hboot 1.55 and Android v4.3, S-On I've been struggling with this for over a day now.

I unlocked and rooted my phone just fine (HTC One on Sprint, 4.3) - but when I flashed a ROM, I flashed Maximus HD, which was apparently an International version and not a Sprint one. I think that messed some things up. After trying a few different ROMs on top of that, nothing works.

Each ROM I flash will "install" correctly, but when it boots to the lock screen, upon unlocking it gives me the HTC splash screen.

I'm convinced that my accidental upgrade to hboot 1.55 is rendering it impossible for me to flash any working ROMs - be it stock or otherwise. I can enter Recovery mode, adb sideload, and flash ROMs, but none of them work.

I've tried Superwipe and then Bad Boyz, but it's the same thing. After installation, it sticks at the HTC splash screen.

So, my options are limited. I think I need to find a way to revert my hboot to 1.44 from 1.55 - that way at least the stock RUU is compatible. However, I can't find any way to do this; since I'm S-On, and I can't access any ROM to mess with settings, I have no idea how to do this, or how to flash a workable ROM in order to switch to S-Off.

Anyone have any ideas. I'm seriously distraught. I just bought this phone, and I love it. I'm so sad that I decided to try this rooting/unlocking/ROM flashing business because it's disrupted my sanity.

Any thoughts or ideas will help immensely. I will give more information if needed. Thanks!
You need to do a factory reset and wipe the Dalvik Cache. What bootloader are you using? TWRP or Clockwork would be examples. I would enter this as a comment but lack the necessary reputation. 
This tread on XDA may be of use. Soft Bricked - XDA