For 3 weeks I have been trying to fix a problem with my PC where when I turn it on, it starts up the fans and lights and then turns off after about 18 seconds and tries to boot again on it's own. I have done a full motherboard swap, hard drive swap to SSD, tried every single possible RAM position I could, with both RAM sticks, tried with GPU in and out, tried with 3 different CPU's (2 different 200ge's and 1 3700x), and have unplugged and then plugged everything right back in at least 5 times. The PC is custom built by me. The GPU, PSU, Hard drives, and RAM all came from an older PC which had a slightly different case (black phantek P400 instead of my new white P400). The only things that have changed between my functional PC and my now dysfunctional PC are the case, motherboard, and CPU. The new CPU is a 3700x, the new motherboard is an Asrock X570 Steel Legend, and the new case is the white Phanteks p400s. Originally I tried it with the Asus Prime x470 Pro, however, I had the same issue, and have swapped that motherboard with the X570 Steel Legend. I have spent way too much time and money troubleshooting this issue, and wonder if anyone else has had this problem and if they have any other solutions which have worked for them. I have got to the point of losing hope and I may just sell all the parts on eBay for a significant loss ): . Here is the part list: GPU: Gtx 1080ti, Cpu: Ryzen 7 3700x or Athlon 200GE, X570 Steel Legend, Corsair Vengeance LPX DDR4 16GB 2 Sticks, EVGA Nex 650G Powersupply, Phanteks P400 Case, Sandisk 1TB SSD or Seagate 2 TB Hard Drive.