Why did the laptop stop seeing the RAM bar?

Question

Electronics

One day, the laptop stopped seeing the memory strips that are inserted into the slot. Prior to this, the slot worked. The laptop was not disassembled, not dropped, not overclocked. I inserted several obviously working slats into the slot - none of them work, although they worked yesterday. I tested them on another laptop - they work.
There is only one slot on the laptop - another 4 GB of memory is simply soldered on the motherboard.
Tried to take out the bios battery, reset the bios settings, disconnect the battery from the mat. fees.
I tried to run memtest - it crashes instantly, or rather it just hangs without having time to start the test. Under linux, I launched memtester - I scanned everything that could be allocated, I did not find any errors.
I thoroughly cleaned the connector and straps with alcohol - there is no effect.

Answer 1

Check the BIOS setting Memory Remapping Feature or something similar:
DRAM Over 4G Remapping
H/W Memory Hole Remapping
Hardware Memory Hole
Memory Hole Remapping
Memory Remap Feature
Memory Remapping Feature
But I'm more inclined that something burned out in the motherboard.