Why does the PC not start after assembly?

Question

Iron

We have the following assembly:
- Ryzen 7 3700x
- Asus Prime x470 PRO
- SSD Samsung EVO 970 PLUS Nvme M.2 500gb
- SSD Samsung EVO 860 SATA 3 500gb
- 1 x RAM Hyperx Predator 16gb 3200 CL16 RGB
- 2 x EVGA GTX 1080 SC SLI (Used checked, tested - working)
- EVGA 850w BQ (Used checked, but I don’t know under what loads)
Everything except the components indicated respectively is absolutely new. When trying to put it all together, I got a headache, depression and a couple of basic questions.
Question 1:
At the first start, the backlight blinked, after that the power button showed no signs of life, subsequent disconnections and inclusions of the power cable repeated the effect from the beginning. In an attempt to identify the problem, I almost rebuilt everything anew, the problem turned out to be related to SSD EVO 860 SATA, if the power cable is connected to this device, then the PC does not breathe. I tried various variations:
- turned on / off the SATA interface along with power
- left only the power supply, the percentage and this SSD
- the power supply is partially modular, I tried to switch the power cable to different connectors with the SATA signature
- there are 4 loops on the power cable itself, I tried each
None of the above solved the problem, so I would like to know how it happened? What happened to the SSD? Who is to blame and where should I go with this problem? (SSD under warranty)
Question 2:
After I identified the first problem, I happily collected everything back, I thought that I also have an M.2 SSD there, so for now I will manage only with them. But unfortunately I came across a black screen with the inscription "No Signal". A selection of related facts:
- coolers on the system unit spin, absolutely everything glows as intended - RAM, video cards, coolers, motherboard
- I tried all available variations with video cards (both in SLI, both without SLI, each separately and in different slots) , but everything is via HDMI, there are no other cables
- the processor heatsink is warm, but the cooler scrolls only once at the time of startup, I hope this means that the processor itself is in order and works, but since it does not get very hot, there is no need to cool it.
- on video cards, coolers twitch strangely every 5 seconds, it looks like they are trying to spin, but something is preventing them, I don’t know how it should be, I’ll just leave it here (the thought of a bad PSU has not left me since the last problem, so I paid attention to this behavior and assigned it potentially to the BP)
- the most key thought - BIOS - I know that the motherboard supports the new generation of Ryzen, but I read that you need to update the firmware to work with them. However, I also read that this motherboard has ASUS EZ Flash 3, which allows you to update the BIOS via a USB flash drive or an Internet connection and naively assumed that I could do this even with a new processor. And now I don’t know what general behavior the PC should have in this situation, is it possible that the black screen is quite normal under these circumstances? And if not, what is wrong? BP? Maybe Nvme M.2 can't be the only drive in the system yet? (sounds crazy, but you never know)
Of course, I don’t have a speaker in addition to everything else, and I didn’t catch any signals at the audio output either, so I can’t even diagnose it completely. In the hard part, it is very weak, so soldering something from improvised means is not for me. There are no neighbors, friends across the road, or just a second PC at hand to test individual components. Only laptop available. From tools: screwdrivers, knives and a hammer. So I didn't do any voltage measurements anywhere. I would be grateful for any help on this issue.

Answer 1

It looks like a short. Crooked assembly, somewhere short on the body. The BP sees this business, it has a short circuit protection.
M.2 is the only hard drive in the system - easily.
I would gut the computer and assemble it "on a breadboard" - that is, the mother lies on an insulated lining (plastic, wood), the minimum necessary for launch is stuck into it. You can start the mother by closing the legs in the connector, to which the Power button is displayed (which it actually does).
If it starts up in this form, it means either a crooked assembly, or the body is barn (I once encountered this, I couldn’t understand for a long time - what ??)

Answer 2

Start with bios. Bring the fee to the service / store, update the BIOS to support your processor.

Answer 3

the most key thought - BIOS - I know that the motherboard supports the new generation of Ryzen, but I read that you need to update the firmware to work with them.

All right, you need to update.

However, I also read that this motherboard has ASUS EZ Flash 3, which allows you to update the BIOS via a USB flash drive or an Internet connection and naively assumed that I could do this even with a new processor

Well, read the instructions for it. For example, here .
The problem is that it's not Flashback, which means you have to get into the BIOS first, which you can't do with a new processor until you upgrade it. So, you need to either find a service that will update your BIOS, or borrow a processor, for example, from a friend. In the US, AMD even sends out athlones for you to flash the BIOS from.

Answer 4

black screen with "No Signal"

This is what the monitor is telling you.
Either the video card to which it is connected did not start, or it simply has several inputs and it looks at the wrong one.