Hi RTorres!
(You prompted me to write here again and to thank SnowDej for all the help he gave me! Thank you man 🙂 )
DONT GIVE UP!
Why? Because the actual solution I found was to put a different CPU in my board. See another poster SambalBij with similar experiences
I bought another machine to swap the boards over (after investigating getting the ROM chip replaced, which is possible but in my case was more expensive). Just as an experiment I tried sticking the CPU form the donor machine in my dead one before ripping out the board, it was a lower spec but same gen (1605)
It did not load the rom from the usb
Fans came up and went down, and it remained stable, no beeps, still black screen.
I restarted without the USB stick and with a GPU and it booted like it always had before i trashed it
*** I put the original CPU back in (1650) and it ran perfectly***
DO BE METHODICAL!
There are so many variables here even if you do try a different CPU
If you can verify everything you're using to test is working first (RAM, CPU, GPU, USB disk etc)
I would be looking for absolute minimum attached to start with
1 stick of ram, no hard disks or cd drives etc
nothing in the expansion slots except a GPU (again an older GPU that can BIOS boot might be useful as opposed to UEFI GPU)
If you're getting beep codes resolve those first
I would try the USB flash last, as in your case you just wanted to upgrade processors
I dont know why this works, but I am sure I am not the only one. Something on the board is hanging the machine before it even gets to boot the USB flash disk
I did not even try the USB again as i was happy to have it back but I bet it would work now. I do know my bootable USBs and I did even try making a bootable CD ROM
I've been using the machine ever since - no damage was done
Good luck!
BTW HP did offer to sell me a new board when I opened a call with them, I am so glad i didnt!