I have extremely low framerate for no apparent reason

I built my PC a couple of years ago and it was going swimmingly. I went out for two weeks and now that I am back the PC runs at maybe 7 frames the moment I try to play any game.

I have no idea what happened. When I played last time it worked. I am not even trying to run some excessive things, Slay the spire 2. The PC struggles to handle even an animated background.

I was never particularly tech savvy so I have no idea what could have happened. Does anyone know what could have caused this?