Question Fans running GPU LEDs on but no display and GPU not detected on motherboard


Nov 6, 2011
Hi! I have 3year old 1080Ti. And I noticed this for most if not all of my gaming. Everytime I start a game (the last game I loaded was GTA 5) the screen goes black. The PC keeps running but the monitor is black. And then I hear an alert sound as if a device was disconnected then reconnected. I tried updating drivers but no go. This is also a relatively clean install of Windows. Probably 2months old.
I then went on to remove the GPU from the motherboard, cleaned all contact points and ports, and reseated the GPU again. This time the computer turns on. Boot and post beeps. GPU fans and LED running. But now it won't display anything. Tried putting the HDMI on the the mobo. I got it to display. But when I checked the device manager, it wouldn't detect the GPU. Any idea? I'm thinking my 4-5 year PSU is to blame. I hope that I am right.

Intel i5-9600k OCd to 4.9GHz
Gigabyte Aorus Z370 Ultra Gaming
Deepcool Gammaxx GT Air Cooler
Gigabyte Aorus 16GB (2x8GB) RGB Memory 3600mHz with demo kit
MSI GTX 1080Ti Gaming X
Seasonic S12II 520w 80+ Bronze PSU