My FPS Just Dropped Off?

So I’ve been playing on my new PC since Friday 9/27 everything runs great on ULTRA settings. Come today, I’m playing for a few hours I go AFK for like 10 minutes. I come back to my FPS drop to 10 so I restart the client still just really bad FPS turn off my PC turn it back on start the game up and still just horrible FPS… anyone have or had the same problem or any tips what to do? Thanks.