My guess is, power-supply gone bad or not supplying something with the correct voltage consistently. Replace it
... a good hypothesis ... many gamers have average (or old) PS and they never consider changing it for a quality brand-name PS ... the Power Supply is a component that a lot of people take for granted and never pay attention to ...
some upgrade their video card for a more powerful one ... which stresses the old average PS ... they put a lot of money into the VC : paying more for a new PS is not in their budget ... consequence : the new VC might not be able to perform in a consistent optimal manner ...
TO the OP : change your PS for a quality brand name one (not below 450 watts) ... even if it does not solve your current problem (

) it can only do good to your machine (if it has been installed by a competent tech) ...