What we be useful is to get a screenshot of your bootloader screen, or boot your phone to the bootloader and post what's on the screen - specifically whether the bootloader is "Locked" or "Unlocked" and whether the phone is S-ON or S-OFF. Do you have a Win PC/laptop with the adb/fastboot tools installed? You can get it here if not:

ADB Guide (updated 2014/11/11)

along with instructions to install.

Reboot phone to bootloader and plug in to PC (so you see FASTBOOT USB on bootloader screen). Open a command prompt window in the adb/fastboot folder on your PC - if in Explorer hold shift + right click, and pick "Open command window here" from context menu.

Then type:

fastboot devices (this is to check fastboot connects to phone ok, it should also return the phone serial number)

If it does, then type:

fastboot getvar all

and post the info the command returns here but scrub out your IMEI number and serial number.

Note that if your bootloader shows "Locked", unfortunately we may end up in the situation where to get phone working again the process involved wipes your phone including the internal SD card. I'm going to do some digging as well, but just letting you know so you're aware of this.

 

Is this a Google Play Edition phone? Curious as to the unlock icon on the HTC splash screen, and the bootloader screen is different as well. Can you do the:

fastboot getvar all

as well and post the results, but scrubbing out your IMEI number and phone serial number.

 

Good stuff. Just be aware that since you have GPE partition setup, you won't be able to flash any HTC Sense based roms as they will not fit in the smaller GPE system partition.