The laptop does not see the RAM after disassembly. What to do?

Question

laptops

Dismantled the laptop to clean from dust and change the thermal paste. Everything went fine, but after assembly, both in the properties of the computer and in the "system information" it says that I have only 2 GB of RAM, although I have two 2 and 8 GB sticks. But the strangest thing is that the CPU-Z program says that there is an 8 GB die in slot No. 3. Why does CPU-Z see it, but not the OS?

Answer 1

And the layout of the bars remained the same? Perhaps the reason is in the different frequency of the bars.
Try swapping the planks in the slots.

Answer 2

bios settings gone wrong

Answer 3

See what the bios says

Answer 4

You pull out the die and wipe the contacts with a pencil eraser (not much). Usually the problem is dirty contacts. If that doesn't work, try the options above.

Answer 5

And it’s possible that it shortened it .. so look, check