Question Aorus b360 gaming 3 wifi

[Nomad666]

Just finished building a new pc right now. As I plug in the power cable, the LEDs on the motherboard flash once and then nothing.
The specs are :

Aorus B360 Gaming 3 Wifi (ATX)
Intel i7 8700k 8th gen
Corsair Vengeance ddr4 3000mhz x2
WD 500GB m.2 SSD
WD purple 2tb HDD
Cooler Master Hyper 212 LED
Gigabyte P650B PSU (650w)

There is no GPU as its an Audio Engineering system. But MOBO booted fine when I checked it in the store with just CPU (with stock cooler) and RAMs on board. But that was done on an inferior PSU.
What's essentially happening is, as soon as I turn the PSU on, the Aorus logo on the south bridge and the onboard LED strip flashes and then kaput. There's nothing. Not even if I just turn the PSU back off and on. Only if I remove the power cable and replug it, it happens again.

Its a friend's pc that I'm building so I kind of want opinions from experienced builders before I start doing random stuff on my own completely.

 

[Nomad666]

Also just realized, on board LEDs don't turn on either. Just the Aorus logo on south bridge and the HD Audio logo. Both flash white and poof.

 

[mdd1963]

Disconnect all drives (SATA power and SATA data connections), and internal USB headers from mainboard...

Drop to one stick of RAM in required slot (testing each alternately)...

Make sure MB's power is connected, both 24 pin and 8 pin ATX12V CPU PWR, using new cables that came w/ your PSU, not any old cables from a previous PSU...

Make sure your sink's case fan is connected to CPU FAN header on MB, or, if using an AIO, that the pump is connected to a correct header as described in manual. (Some wedge it into a fan header when it requires USB, or connection to CPU FAN or AIO PUMP, or, vice versa..

the only critical case wires are the PWR SW, which need to be connected to the two PWR SW pins on the MB...

 

[Nomad666]

Tried removing SSD and Wifi card and Heat Sink and RAMs individually.
Tried with two new Corsair Vengeance 3000mhz RAMs and then with my old G. Skill Ripjaws 2400mhz one.
Also tried to use my old 500W PSU which runs absolutely fine on my desktop.
Haven't tried disconnecting HDD yet so will do that now.

Also if its any help, I have always sucked in setting up the case wires thanks to my stubby fingers. Is there a particular way the wires are to be connected? I received a Gigabyte G connector and put the wires in as the names suggested. I was confused about whether to use the PLED+ and PLED- pins or the Pwr_LED+ and PWR_LED- ones. I will tweak around that too now coz I think there might have been a mistake there. But shouldn't the board get power regardless of those?

 

[Nomad666]

Tried without HDD, tried switching around the case wires.
Turns out, now that I have plugged the pwr led wires into the PLED slots, the colour of the light in the Aorus logo has turned Turquoise instead of the White it flashed now. But it still goes out as quick.

 

[Nomad666]

Also the light wont flash if i just replug the cable. Only happens when I remove the cable, hold down power button for a while to discharge, and then put the cable back in.

This is sooo damn frustrating.