Question Z390 Aorus Elite not booting

[Decius88]

So I am building a whole new system, every part being completely brand new. I hooked everything up, triple checked all the connections and go to turn it on and it doesn't boot. Instead when I flip the PSU switch on the motherboard flashes its LED and when I press the power button on the case everything starts up at first seeming to be fine. I look on the board and the LED light for CPU is solid red and after about 20 seconds the fans start to slow down and the system restarts itself only to repeat the process. As the board LED for CPU is solid red I first thought something was wrong with the CPU and got a replacement but that did not solve anything. I think the motherboard might be faulty but i'm not sure. I don't want to have to replace the board to find out it wasn't the issue either. Any ideas?

Hardware:
Board: Gigabyte Z390 AORUS Elite (Intel LGA1151/Z390/ATX/2xM.2/Realtek ALC1220/RGB Fusion/Gaming Motherboard)
CPU: intel i9 9900k 8 Cores up to 5.0 GHz Turbo Unlocked LGA1151 300 Series 95W
GPU: Geforce RTX 2080 graphics 08G Duel-Fan OC Edition GDDR6 HDMI DP 1.4 USB Type-C
SSD: Samsung 970 Evo plus SSD 250 GB, Samsung 970 Evo plus SSD 1 TB
HD: Seagate Firecuda 2 TB 3.5-Inch SATA 6Gb/s 64MB Cache Internal Hard Drive
RAM: Corsair Dominator Platinum RGB 32GB (4x8GB) DDR4 3200 (PC4-25600) C16 1.35V Desktop Memory - Black
PSU: Corsair CP-9020180-NA RMX Series RM850x 80 Plus Gold Fully Modular ATX Power Supply
Case: Corsair Obsidian 500D RGB SE Mid-Tower Case, 3 RGB Fans, Smoked Tempered Glass, Aluminum Trim-Integrated Commander PRO Fan - CC-9011139-WW

 

[boju]

What's your cpu cooler and is it properly connected to the cpu_fan header on the mobo? If cpu_fan header isn't connected, the cpu won't operate.

 

[Decius88]

I am using a Noctua NH-D15, Premium CPU Cooler with 2x NF-A15 PWM 140mm Fans for my CPU cooler, and it is connected and powered. The fan runs on it. One thing I didn't specify before was when the fans slow down before powering off it is only the PSU fan. the other fans continue to run at full speed until the system powers off and restarts.