Question Can’t boot my system when you plugged in

Oct 13, 2019
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So. This is my very first build, and I’ve done it from scratch. Specs, if you’re concerned:
CPU:Ryzen 5 2600 non-x w/ stock cool
Mobo: Msi b450 a-pro
Gpu: gigabyte rx 570 gaming oc, second hand
Ram:g.skill sniper x ddr4 3200mhz
Psu: an old 1200w thermaltake thing. Found it second hand.
Ssd: 240gb patriot burst 32mb cache
Hdd: 1tb wd blue 7200rpm 64mb cache
Case: rosewill nautilus

So, the issue is that when I plug in the gpu and connect it to the power, the computer sometimes turns on for half a second, with all the lights and thingymajigs. And then it crashes. But when the gpu power connector is removed, the system turns on, and even the gpu rgb is on, since I assume it’s pulling the power from the mobo. It isn’t pcie connector on the motherboard, because the system boots fine when I plug in my old Radeon HD 5000 series card. The guy who sold the psu has tested it and I’ve seen it working in front on my eyes (for his system, that is). Please help i need all the support I can get. Thank you so much.
 
Oct 13, 2019
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Actually, my system doesn’t tend to freeze or restart. It just flickers for one second with the gpu plugged in. When I replace the gpu the system runs beautifully. I even set the whole thing up and downloaded all my preferred apes on windows! Just that rx 570...
I don’t think it’s the gpu’s fault. Also, one trying I forgot to mention; my psu, being semi modular, has 3 cables coming out of the non-modular part. The mobo power (20+4), the cpu power (4+4) and another random plug. It is a 8 pin but doesn’t seem like it is for pcie power...so I had switched the cpu power (unknowingly) with the gpu power and plugged the other one into the cpu. The system does that flash for a second and crash thing again. Do I need a different modular cable? ‘Cause the guy I bought it from only provided 2 extra sata connectors. Any help is appreciated.
 

kaehligj

Prominent
Mar 15, 2018
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If the setup runs fine with one GPU, but not with the other, you have a problem with that GPU, no nonsense.

It does not help you if you get off discussion and talk 8pin cables.
That GPU is deadening your system and have a problem. Period.

If the GPU has an 8pin, 6pin or 4pin pwr connector, it is there for a reason and must be powered from the PSU.
This possible missing pwr MAY be the problem with that GPU, but you have already isolated this GPU to cause your system to crash.
 
Oct 13, 2019
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No the other gpu is a Radeon HD 5000 series, which doesn’t need any external power. My rx 570 was also tested in front of my own eyes and the seller had played some games with it plugged in to prove that it works: it is not the gpu and I’m sure of it I just don’t know how to fix this issue. All help is appreciated
 

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