Hello and welcome to Techspot.
Sounds like something is overheating to me.
Check your cpu temps, also cleanout any dust bunnies from inside you computer.
If you remove the side panel from your case, you can aim a desk fan into your case. If the situation improves, then it`s almost certainly an overheating problem, possibly your videocard.
Some extra case fans may also improve the situation.
Regards Howard :wave: :wave: