[SOLVED] Nothing works and I don't know why

[Sajuke]

So I decided to put together a new system in an ITX case I have but its caused me nothing but a headache since.
I started with;
Gigabyte B550I AORUS PRO AX Motherboard
AMD Ryzen 3 3100 Processor
Corsair CMK16GX4M2B3200C16 Vengeance LPX 16 GB (2 x 8 GB) DDR4 3200 MHz C16 XMP 2.0 High Performance Desktop Memory Kit, Black
Corsair MP600, Force Series, 500GB High-Speed Gen 4 Pcie x4, NVMe M.2 SSD
Gigabyte GeForce GTX 1650 OC 4GB GDDR6 Graphics Card
and a corsair 450w psu that was already in the case
After putting everything together the system would not power at all, no lights from the mobo, nothing. I tested the psu and it seemed fine, I tested the system outside the case with no change. Hard to diagnose a computer that doesn't power at all so I got another psu (600w this time) and that made no difference either.
So I figured the motherboard was a dud and got it replaced only to have the same problem.
I replaced the motherboard again with ASRock B550 PHANTOM GAMING-ITX . This one lights up when the power is connected but still will not actually switch on.
I've tried every combination of basic components only, one ram module only, jumping the power switch pins with a screwdriver all for nothing.
Could a bad processor cause this? If not then what else could cause this?

 

[rgd1101]

check for bend pin on the cpu?

 

[Balefire]

Check to see if you installed the case power buttons correctly
in my opinion, this is most often done wrong. it's also very easy to fix
simply look at your mother board's manual and make sure all the cables are connected where they're supposed to be

if this doesnt help then make certain you cpu fan/pump is connected correctly... it's rare, but i did hear from a friend that his pc wouldnt start because he didnt plug in the fan correctly... it's some sort of safety feature

 

[Paperdoc]

Balefire's last item is correct, and here is an explanation. All mobo fan headers have a secondary function - monitoring the speed signal coming back from its fan for fan FAILURE (detected as NO speed signal, or sometimes a speed too low). Failure normally causes a warning to your screen so you can fix the problem. But all mobos do much more for the CPU_FAN header because no cooling could cause overheating so bad it permanently damages the expensive CPU chip. If there is no CPU fan speed signal at that header (bad fan that is stalled, or bad connection for no signal, or NO fan plugged in there), MOST will do more that just issue the screen message. Many will just shut down the entire system pretty quickly without even waiting for the CPU temperature sensor to indicate a hot CPU. And some will not even allow the system to boot up at all if there is no CPU_FAN speed signal detected within a very few seconds of trying to start.

On most systems, you connect the CPU cooler to the CPU_FAN header, but in some situations that is not done deliberately. Some use a fan plugged into a PSU output instead of the mobo header and leave the CPU_FAN header unused. That can cause you problem. If that is your intent, there is a way to defeat this protection system. Connect any fan to the CPU_AFN header temporarily and it should be able to boot if that really was your problem. If that works, go into BIOS Setup to where the CPU_FAN header is configured. Try to find an option to IGNORE the fan speed or turn off the fan control for that header, and that can disable the failure monitor for that header.

If you have installed a liquid-cooled (AIO) system, where you plug things in can also cause this problem. If that is your situation, review the instructions for the AIO system and do what its makers say - do not try a "universal" method because there is none. All AIO systems are different.