Well, actually looks a bit worse. You said that the ram from the "broken unit" is not working in the "working unit".   So... lets put together the various facts : The motherboard doesn't work with its ram AND with known working ram The ram of the messy unit does NOT work in a working unit The gpu is ok   I'm going to muse the following : some power spike / surge / whatever damaged the power distribution to the dimms and at the same time damaged the dimms. Was it under ups ?   You may want to test the "problematic dimms" one by one using the working unit, to see if they are all causing the error , or just some. I think you'll need a new mb, the cpus would need to be tested to play safe prior to sourcing the mb. And I would , personally to play safe, keep the psu outs under a bench for a day to make sure the rails all do what they need constantly.   This is, anyway, a personal opinion.
The machine makes normal sounds during boot up but nothing gets displayed to the monitor. I tried all three outputs from the Quadro K4200 card. I am fairly sure cable and monitor is ok as they work fine with another 7910T system I have. Do I have to remove the card and put another one in to debug? Or is there a way to attach a monitor to some other part of the workstation. I don't see any VGA output on the back though.
Dell 7910T with Nvidia Quadro K4200 gives black screen