New build, no life.. HELP!!

Hi, So I bought the following for my son, having been told from the store that it was all compatible:

ASRock320M-HDV r4 mobo
AMD Ryzen5 3600
Corsair 8GB DDR4 Vengeance LPX 2666MHz Memory
PowerColor AMD Radeon RX 580 8GB Red Dragon V2 Graphics Card
WD Green 240GB M.2 2280 SATA 3D NAND SSD/Solid State Drive
700w Power Supply

Built it all a few weeks ago with my son (it's his first gaming PC), turned it on, nothing on the monitor, no power on keyboard. Started swapping bits out with my own PC to try and troubleshoot it. Swapped everything except CPU, didn't want to take mine out. nothing. Figured the problem was either mobo or CPU. Read that the bios needed an update for the Ryzen5. sent mobo and CPU back to company who tested them and sait bios was up to date and both worked. got them back today, rebuilt, same thing...

The fans spin up - CPU, case and GPU fans, then settle in to a cycle of about 5 seconds of medium fan, then 5 seconds of low fan with no GPU fans, repeat.

I am completely stuck - any ideas anybody?

Thanks

It sounds like the RAM isn't being recognized properly, likely not seated all the
way into the slot as Threedee noted. This is quite common with new boards as the new RAM slots are
a very snug fit.

Edited by Xaltar - 05 Jun 2020 at 1:06am

The CPU power is always either 4 or 8 pin these days on consumer boards. The only
cable that is a 6 pin or 6+2 pin is the PCIe power for a GPU or other PCIe device
that requires more than the 75w provided by the PCIe slot.

I don't think the issue is because of a neglected CPU power cable however, I tested
on a few of my own systems and when the CPU power is not attached the fans spin
up to full speed and just stay there, no slow down, no power cycling. Installing
the RAM improperly (not pushed in all the way) however did produce similar
symptoms which is why I suggested the OP start looking there.

Not sure how to edit my post. So I did few mistakes with my RAM. 1st. I put in wrong 1-3 slots (was so sad that XMP is not working, reaching only 2600MHz). 2nd. When I put in 2-4, one of the RAM module were sticks out from the left side(not sure if this right word in english). So it didnt fit from one side where has no clip. We saw it later. I guess is experience, when you know where to push could be easier. I read in reddit "Slide the ram into the side without the clip first."