Why is one of the DDR-3 ports not working?

Question

RAM

The problem is this:
I put an additional disk (SSD) in the system unit, after I started it, I got cyclic reboots, between them an infinite number of short BIOS beeps. For my BIOS (AMI) read that this means a power problem.
To exclude everything that is possible, I consistently turned off all the components. It helped to pull out one of the two slats of RAM. The computer has started.
Empirically, it turned out that when you install a RAM stick in one of four of the slots, the computer goes into a cyclic reboot, the BIOS beeps endlessly.
At the moment, I installed both brackets in the other two single-color connectors on the motherboard, the computer seems to work without problems. The memory test also passes without errors.
What could be the problem?
Config: Gigabyte GA-H77-DS3H, Kingston 2x4Gb 1333 Mhz memory, Intel i5 3550, 550W power supply known to be good... the rest doesn't really matter...

Answer 1

There may be several reasons.
1. During disassembly, the controller was damaged by static.
2. Somewhere in the area of ​​\u200b\u200bRAM slots on the motherboard, soldering flew off (the track broke off).
3. Problem with contacts (oxidized, bent or fell off).
I think the second reason is the most likely.