[One (M7) Q&A, Help & Troubleshooting] brasstongue:
I recently upgraded to an HTC One, on Verizon in the US. I promptly used rumrunner s-off to get S-OFF, unlock the bootloader, and obtain root. I also flashed the latest ClockworkMod recovery, with the intent of installing CyanogenMod, but decided I'd try out the stock ROM for a few days first, since my old phone was still on Gingerbread.

Everything was working fine until I decided to remove some Verizon bloatware. While I did back up each app before removing it, I forgot to make a nandroid backup. I only removed things that seemed nonessential -- such as the NFL Mobile app, Slacker radio, and My Verizon, which I'd also removed without issue on my old phone -- but apparently that was not the case, as after rebooting, I got stuck on the Verizon logo during the boot sequence.

I then attempted to perform a factory reset in CWMR, and it appeared to be stuck on "wiping cache", so -- like the impatient idiot I clearly am, as I later found a few threads explaining that this part of the reset process can just take a very long time -- I rebooted the phone to try again. This resulted in CWMR throwing errors about failing to mount several partitions, but it finally seemed to finish the reset on the second try. However, upon reboot, it just sat at the HTC logo forever.

After about an hour, and no success in finding anything on the internet indicating that it should take this long to boot up after a reset, I powered the phone off and back on again. After rebooting, the bootloader screen displayed "OS" in red followed by some random symbols. I could still get into recovery, and could still access the device with fastboot, so I decided to try to reflash the stock ROM, using the RUU zip found here.

Due to some problem (this was all about 6 hours ago while I was at work, and I was quite frustrated at this point, so I don't remember what exactly was the problem here) and based on the advice of another forum thread, I decided to try TWRP instead of CWM. But, TWRP wouldn't go any further than its logo splash screen, so I re-flashed CWM. Afterwards, my phone went into a reboot loop -- the HTC logo comes up, the phone vibrates shortly, and then after a few seconds the screen turns off and it does the same thing over again. If I hold the power button down for long enough, it will power down, but if I try to turn it back on, it will either go into the loop again, or just sit at the HTC logo (left it there for upwards of an hour at one point).

I have found several threads about similar boot loop issues, but as I can't get into hboot/fastboot or recovery, I can't try to apply any of the solutions. I cannot connect from my computer with fastboot or adb -- "devices" lists nothing, and all other commands return either "error: no device found" or "waiting for device". No amount of power+volume down makes any difference, nor does holding the phone under a bright light as several threads suggested. Occasionally it will go to a black screen (not off, just black) that maybe it thinks is the bootloader menu, but it doesn't display anything, and after about 30 seconds it will reboot itself.

Does anyone have any suggestions for getting into recovery and trying to reflash.... something?

Alternatively, if I return it to Verizon at this point, will they be able to tell that it's rooted/unlocked/S-OFF?

Any ideas would be much appreciated!