Artifacts video + audio

Hello,
Artifacts appear in games (not at max load) After they appear (small multi-colored squares of 6 each), the card is cut off, every time after that it immediately rebooted and everything was fine. Often I hear sound artifacts when altab, or switching between applications. What to pay attention to? Build i7 6700k + 980 ti + 16gb (one die). Artifacts appear as randomly as possible at max load, there were current a couple of times. I think on the PSU, I took a deshman 2 years ago, Ksas for 800 watts, the assembly consumes (according to the bequiet calculator) max 500 watts. A couple of times artifacts appeared in the browser when switching between programs. What could be the problem? Well, what to check first of all, I myself think to immediately change the bp, because it makes noise and does not inspire confidence. Temperature under loads max ~ 70 degrees. In normal tasks 50