Hi, my sons R9 390 on an Asus Sabertooth motherboard stop working and pc refused to boot, so I automatically thought his GPU had died and ordered him a new one (RX 6600). I installed it and same thing is happening as before. MB will beep once for good post, show the bios splash screen then lose signal. I tried my 2080 in it and it booted into Windows first time. I tried the 6600 in my rig which is newer (X570) and it booted first time. I have no idea why it won't work on his AM3+ board. I have also tried all 3 DP ports and HDMI but still loses signal. I've been building PC's for decades but this has me stumped and I need help, I really don't want to give him my 2080.