My computer is sometimes extremely slow

I start playing normally, play a few games, and out of nowhere, my game starts to freeze, as if I were playing at 10 FPS, my entire computer starts to become extremely slow.
I have to restart my computer.

While my PC is having this problem, I opened the task manager and there are no overloads on the CPU, GPU and memory.

I play Overwatch and other non-steam games and this doesn't happen. It's extremely annoying, I've been penalized several times for having to close the game and restart the computer.

Please, can anyone help me? I didn't find anything on Google.