I'm glad you got it working, however, they are wrong. It's not surprising, since about 50% of the time that I listen to something one of the repair shop employees says to a customer or one of the geek squad, micro center type technicians, it's often blatantly false.
Any employee who told you that memory should be populated starting at the closest slot to the CPU should be fired, for being an idiot who hasn't the slightest clue what they are talking about.
Take a look at EVERY DDR4 motherboard user manual for any motherboard that has four DIMMs. They will ALL show the second and fourth slots as the two that are required to be populated FIRST, when using only two DIMMs and will always either show the second slot over from the CPU being populated first if only one DIMM is used, or showing the FURTHEST slot away from the CPU in the case of ASUS X570 motherboards.
This is not up for argument, by anybody. Repair shop or not. It is the standard and is employed by all motherboard manufacturers across the board. Well, at the very least, it is definitely employed by all the major manufacturers. ASUS, Gigabyte, MSI, ASRock, Supermicro, EVGA, ALL designate the same population recommendations EXCEPT for the very recent ASUS X570 motherboards as I've explained. Even then, they STILL recommend using the second and fourth slots, they just switched which slots they recommend using first when only one DIMM is used.
This is not because manufacturers just happen to "like" those slots. It's because that is the way the architecture for dual channel motherboards, both DDR4 and MOST DDR3 assuming motherboards released after memory designs changed from low density chips to high density chips, and from what I've seen, even the majority of those from before that on the DDR3 platform. For DDR4, there are ZERO exceptions from what I have seen and there have been extensive arguments by those who think they know better based on some misleading information contained in some user manuals however in ALL of the user manuals the population rules graphic shows exactly the same thing. And, based on some memory deep dive documentation we've seen, and further conversations with helpful individuals who happen to have engineering degrees in this area, we know it to be true.
I urge you to look at the motherboard manual memory section and see that the graphic for the memory population shows you what I am saying. I further urge you to look at the manuals for OTHER motherboards as well, to see that they show the same thing.
I cannot tell you that there is a problem with any specific part or component. I can only tell you what USUALLY causes these type issues and it's usually either a bent pin on the CPU or motherboard (Depending on whether it's AMD or Intel since Intel has the pins on the board and AMD has the pins on the CPU), or a motherboard with some other fault, or bad memory, or memory that is not a matched set, or a CPU cooler that is unevenly tightened around the socket causing the CPU to "cock" in the socket which can cause it to either lose a connection on one of the pins or short to something it is not supposed to be touching.
In some cases, a bad BIOS image or faulty BIOS version could cause some similar issues. Aside from that, I'm not sure there is much else that can cause this and in every case I've seen where the memory would not work correctly when populated in the way it is supposed to be, it was one of those things.
Here are some similar examples.
https://forums.tomshardware.com/thr...al-channel-ram-problem.3483682/#post-21058497
https://forums.tomshardware.com/thr...0-asus-b450-prime-plus.3522335/#post-21281647
As indicated by one of our resident memory engineers, in Post #5 here:
https://forums.tomshardware.com/thr...-2nd-and-4th-slot-first.3195865/post-19720591
I would FIRST try putting the memory in slots 2 and 4. Then double check that there are no bent pins. Make sure the CPU cooler is tightened EVENLY all the way around with no one spot tighter than another. Do not tighten any one fastener all the way in one step. Tighten in increments going around the socket until all fasteners are "snug" but not "clamped down" overly tight. Make sure you have the latest BIOS version before any of that.
Then, this.
BIOS Hard Reset procedure
Power off the unit, switch the PSU off and unplug the PSU cord from either the wall or the power supply.
Remove the motherboard CMOS battery for five minutes. In some cases it may be necessary to remove the graphics card to access the CMOS battery.
During that five minutes, press the power button on the case for 30 seconds. After the five minutes is up, reinstall the CMOS battery making sure to insert it with the correct side up just as it came out.
If you had to remove the graphics card you can now reinstall it, but remember to reconnect your power cables if there were any attached to it as well as your display cable.
Now, plug the power supply cable back in, switch the PSU back on and power up the system. It should display the POST screen and the options to enter CMOS/BIOS setup. Enter the bios setup program and reconfigure the boot settings for either the Windows boot manager or for legacy systems, the drive your OS is installed on if necessary.
Save settings and exit. If the system will POST and boot then you can move forward from there including going back into the bios and configuring any other custom settings you may need to configure such as Memory XMP profile settings, custom fan profile settings or other specific settings you may have previously had configured that were wiped out by resetting the CMOS.
In some cases it may be necessary when you go into the BIOS after a reset, to load the Optimal default or Default values and then save settings, to actually get the hardware tables to reset in the boot manager.
It is probably also worth mentioning that for anything that might require an attempt to DO a hard reset in the first place, it is a GOOD IDEA to try a different type of display as many systems will not work properly for some reason with displayport configurations. It is worth trying HDMI if you are having no display or lack of visual ability to enter the BIOS, or no signal messages.