7920 boot issue ( flexbay nvme)

I have an issue with a 7920 which was working until I messed about with it 😕 may own bad . 

Now I'm stumped and looking for an assist.. I fitted the rear four HDD setup and fitted non original to the spec nvme carriers flex bays on the front. 

Have eventually got the thing working. 

Except .. 

Crucially 

It won't boot from power up ...

It will boot IF

You choose to select the device as you would say you were choosing to boot from dvd / usb etc

Otherwise it goes into diagnostics  

Very frustrating.

Any help would be appreciated.

I have taken every non essential thing out of the pc except it's graphics card ( which I've actually borrowed for another meantime) .

Ps has anyone ever worked out how to get the rebar thing working on a 7920

Many thanks