Dell R840 Stuck at configuring memory after memory upgrade.

So, we have a bunch of R740 which has been decommissioned. We are planning to cannibalize the RAM to our production R840 servers.

For the record, the RAM specification is same between those 2 models, it is 64GB DDR4 RDIMMs, same ranks, everything checks out. Original configuration of R840 is 8 DIMMS, we are trying to fill up all additional 40 slots thus making the total to 3TB RAM capacity.

Now, when we install the RAM, upon power up, we are greeted with.

"Initiliazing Intel ultra path.....",

then "Configuring memory"

and that is where it stops. At the splash screen, no progress whatsoever for 4 5 hours, and no keyboard or mouse input is registered. Checked in iDRAC and we even sent the TSR logs to support, and it didn't return any positive result.  

If any of the DIMMs is failing/failed, should the server supposed to be able to identify and notify which one is failing, no?

Troubleshooting done:

1. Power deep drain - same result

2. Return back to original config - able to boot properly

3. Install to white slots first and boot up - failed to boot, stuck at configuring memory

Is there any setting I need to enable to allow the BIOS to notify which RAM is failing?
Of at least notify what is going on?