4 RAM slots but 2 not working - Old issue - HP Elite Desk 800 G1

[rszvsn]

Regarding this issue - if anyone finds it, I came across it as well. This may be a possible solution for you.
https://h30434.www3.hp.com/t5/Desktop-Hardware-and-Upgrade-Questions/4-RAM-slots-but-2-not-working/t...
It is not grounding issue, not grounding yourself has killed probably very few computers. 
I discovered that the pins on the CPU socket in the right bottom side are responsible with reading memory slots correctly. 
I had 2 PCs with the exact same issue, one was reading only dim1 and dim2, the other was reading dim3 and dim4. 
The solution is simple, check if there are any bent pins and try positioning them back in that CPU socket area. 
1st pc - had a small dust thread in the socket that somehow managed to very very slightly make one of the pins, not do full contact. Cleaned the dust with air, and only very slightly pushed the pin up - issue solved. 
2nd pc had a really bent pin in the CPU socket, somehow whoever did installation of the CPU managed to pull one pin backwards. Bent the pin back and issue solved as well. 

[BeemerBiker]

I have had to straighten pins as well as remove heat sink material from pins and it is no easy task.  To remove a used CPU, I turn the motherboard over and let the CPU fall into my hand.  To insert a new CPU, I use a small suction cup, the type that comes with appliance type light bulbs in a retail package.  Leaking coolant generally makes a motherboard un-salvageable.