SOLVED thanks to an article by MIKE1986! Awesome
Article is here : http://android-revolution-hd.blogspo...a-htc-one.html
Great dev and great article for anyone stick with my problem
I attempted to flash a custom ROM on my One, doing the usual, installing custom Recovery, factory reset, then install the ROM, but the phone simply reboots to HBOOT every time I reboot after installing the ROM
It seems there is something wrong with the internal storage space, and i've tried reformatting with philz recovery and twrp and keep having the same problem.
I've had Venom ROM on, i'm S-OFF, went back to stock, have latest firmware, wiped to install custom ROM again, now this problem.
I've tried searching XDA and the interweb to no avail so i'm here asking for any and all advice.