My Dell 5820 has been happy for some time now thanks to some help from here - until I decided to add another brand new 16GB of memory to the existing 64GB. Restarting caused a double beep and a startup blinking code indicating faulty memory.

So removed the new module and restarted. Another faulty memory error! Removed all the chips one by one and same each time. Put a single stick in DIMM1 and restarted. Nothing just a blank screen no logo - after about 50 secs it rebooted itself and this kept happening ad infinitum.

After consulting Dell docs online, i removed all the cards except video (RTX4000) did the residual power clear procedure and restarted with one stick in DIMM1. This time the logo came up and after a few self restarts got to to the Win 10 (20H1) logon screen.

Great! However I quickly found that I was unable to add any more of the memory I had taken out back in, as soon as I did got two beeps and a memory faulty error. I can add any size memory module into DIMM1 (8, 16 or 32) and it's happy but not another in of the same size into DIMM2 where it should go or anywhere else that's valid. I also changed the video card to a low-end Firepro but no change.

Any ideas would be appreciated. I'd like to fix it myself if possible but it is under warranty if needed.

Also note that the Win 11 'acceptable' processor list does NOT include any W-21nn series! That's not good news for many if it stays like that. And I don't use Secure Boot as I end up looking at a blank screen that will not respond to any keys. Eventually there are a couple of secs of spinning cursor then the logon screen