new build [help] new build won't post

[Tangybuttz]

This is my first build, here are the specs:

 

CPU: AMD Ryzen 5 1600

MOBO: Gigabyte AB350 Gaming 3 

RAM: Corsair LPX 3000 2x4GB

GPU: Gigabyte GTX 1060 WF2 6GB

PSU: EVGA Novatech 2 650w

HD: Samsung 960 EVO m.2

 

I've assembled the PC, and it did POST initially and went to BIOS. Now the machine will not POST, no output to the display at all. The fans spin up, there's an LED marked CPU on the mobo which lights up solid red, then an LED marked DRAM which flashes red briefly, then the machine reboots and does the same again. 

 

I've already cleared the CMOS multiple times, and I've tried 1 and 2 sticks of RAM in every slot configuration imagineable. I've also reseated the power cables and the graphics card. 

 

The mobo manual isn't very clear on the meaning of the LEDS, I've attached a screenshot of the relevant page in the manual. 

 

Any ideas?