Bit of a weird situation here.
My brother in law wanted help building his pc, so we purchased the parts online and they all arrived.
Disclaimer: committed the sin of putting everything in before testing.
When we tried to power it up, it would go for a second and then power down.
I then started to cycle through parts that it could be, replacing the power supply with mine, still did the same thing.
I ended up basically replacing every part of the pc with something from mine, all apart from the motherboard itself and still nothing.
So my assumption then became that it was the motherboard at fault.
We sent the motherboard back for testing and they have come back saying that the motherboard works fine and they can't replicate the issue.
So at this point I am completely stumped as to what could be the problem, I used every part of my current pc that I know for a fact works, the only part I didn't use was the motherboard and the case.
Parts list:
Motherboard: Gigabyte H370 HD3
CPU: I7 7700k
RAM: HyperX Fury ddr4
Power Supply: 550W (tried with a 1000w as well)
Graphics Card: 2060 Super