I'm having the exact same issue, monitor and kbm wont turn on but other than that everything in the case sounds like its running fine. I had 2 Corsair LPX 8gb ddr4 at 3000mhz and decided to buy 2 more 8gb sticks, corsair lpx ddr4 at 2666mhz. I tried using only new ram, both sticks and then a single stick but monitor and kbm wouldnt start working, I went to BIOS with my old sticks and set the ram speed to auto and tried again but nothing, I am on an ASUS B450 something, also running a ryzen 5 3600 and a 1660 which is kinda mad