I just re-read your thread, and this sounds like a hardware problem.
Your phone was completely stock and under warranty, but you unlocked bootloader with a bootlooping 100% stock untampered phone
And the above information in red, doesn't sound interesting at all
Try reflashing your firmware again firmware_5.12.707.104_signed.zip
Since you are S-ON, you will need to relock bootloader to flash it:
fastboot oem lock
fastboot oem rebootRUU
fastboot flash zip firmware_5.12.707.104_signed.zip
fastboot flash zip firmware_5.12.707.104_signed.zip <- yes, TWICE !!
then check if baseband came back.
you would then have to unlock again and reflash TWRP.
and forget about the 'usb-otg' since you don't have one attached, it's not going to wipe it.
To completely format the relevant partitions, you do the following in TWRP:
1) "Format Data", that will format /data and internal storage
2) Advanced Wipe -> /system and /cache, that will format /system and /cache
3) reboot to recovery
then you can push the ROM again and install it.
AND NOW _ GREAT NEWS!!!!
I followed the steps you gave and then waited anxiously - until finally the phone rebooted and is now working - !!!
This is awesome and I appreciate your perseverance and help getting me through this experience!
I have a final few questions - maybe you can tell me:
- How do I try to prevent this happening again - do I just keep this back up file in TWRP?
- Is there anyway to get/flash the stock ROM - or doesn't it make any difference ( I have not explored this one yet)?
- Is there some way I can return phone to LOCKED and get rid of Tampered?
- I also tried to factory reset the phone through the settings menu - and it went back into TWRP - is there a reason for this? How do I factory reset and then restore from HTC Backup/restore?
and finally - will I receive notifications of software and other OS updates - such as sense etc - OTA?
And again, and again - thank you thank you thank you to everyone that helped get me and this great phone through this!