Need some serious help.

Hello, Recently my PC has been running like shit. I have a pretty decent gaming pc that used to run completely fine. Now, It stutters constantly when I'm in games. I have legit no idea as to why this is going on. Does anyone have any solve for this issue?

MORE DETAIL:
I used to run GTA V at a solid 75 fps, even when I was getting into shootouts, blowing stuff up, or crashing cars. The game still ran fine. Now, I'm experiencing FPS drops and stutters. Does anyone know how to fix this issue?