@mazzinia_ @bradthetechnut Taking a crack at this again because its been sitting around for months now and I wanna make sure its dead before dumpstering it. I have now completely removed everything from the case and am running it bare on my workbench (with a silicone mat under it). The only things connected are the 3 power supply headers, jumper wires to the remote power switch to start it and the intrusion switch that is held down with tape(and I've tested without). I have hooked an oscilloscope up to the rails of the power supply and don't see anything happening on there. I have also tested each wire individually and it all seems fine. I am still getting the same results sadly.

Thanks again!

@user_f63187​ sad to hear. So on a bench ... the psu looks fine ... mm

Have you considered trying to bypass entirely the intrusion detection switch ( lets imagine is faulty and tape or not, is not closing the contacts ) ?

@mazzinia_​ I tried jumpering it and it didn't work I tested continuity with a multimeter and it seems to open and close fine. 

@user_f63187​  this one has been a really weird issue... I mean, I reread and you changed motherboard, cpu , ram , even tried a different psu and the issue kept identical

now is stripped on a bench, excluding the case from the equation... only thing that seems be the same as before would be the power button harness ...

@mazzinia_​ I have removed the power button harness for the last few tests I'm using a separate button across the "remote pwr" pins on the motherboard. At this point I might just chalk this up to several bad batches of parts. It makes absolutely no sense that it is still not working unless there was a short or something that fried each new component I installed the second I ran the first test with it.

@user_f63187​ technically is possible. That you kept receiving faulty parts makes for a lot of bad luck and the chances should be slim. That something in the case damaged the mb and as a consequence damaged the replacement board/s is way more possible

I'd recycle the thing and start over with a unit that comes with a 30-day return policy and/or a one-year warranty (ebay open box or certified refurbished).

I'm baffled as to why it wouldn't work.  The only thing we haven't talked about is the outlet.  During testing, was the PSU plugged straight into a wall outlet or a UPS?  Wall outlet preferred for testing purposes.

Since it won't let you into BIOS, then it likely won't let you into the F12 Boot & Diagnostics either.  Otherwise, we could say run diagnostics and see what it comes up with.

I have exactly the same issue here on my Dell 7920. I cycled through 3 CPUs, 2 GPUs, and 12 sticks of DRAM. No POST. I replaced the MOBO and changed the PDU backplane. All power cables. Wall outlet changes. I have never had this kind of no-post issue. By the way, all my CPUs and GPUs plus rams are good and verified. Anyone with more leads?

The only thing not discussed in this thread is make sure the SSD/HDD didn't fail.  Might want to try a new one.  Other than that, I'm out of ideas for now.

If not already, start by testing or replacing the size 2032 CMOS battery.  Even if the extra MB's came with batteries, sellers never make sure they're any good.

A bad battery affects BIOS and therefore PC operation.