problem with gigabyte radeon hd 7950 video card

I'll say right away that I understand all this badly, but I had such a problem, probably for a year now, namely
in games, that is, when the video card starts to work hard, it can suddenly turn off, or I don’t know what to call it, in general it stops working hard because of which the FPS in games drops to 0, and as I noticed "shutdown" video card occurs at the moment when, for example, in the Witcher 3 game, I switch from the menu or the card (that is, the video card is logically unloaded) back into the game (when the card is loaded), this does not happen immediately, but after the time has expired, maybe in an hour , maybe after 3, and maybe after 20 minutes ... only computer overloading helps ... in quiet mode the viduha heats up to 40 degrees, in the witcher a maximum of 73 ... also noticed, let's say the viduha passed out, I quit the game, I can sit quietly in the browser, watch videos on YouTube, but sometimes the videos start to crash, stripes and artifacts appear on the screen,again, the overload of the computer fixes everything, in fact, I took out the viduhu, untwisted it, cleaned it from dust (I never changed the thermal paste) but nothing helps me, before there was another problem, the screen could go out during the game and did not turn on at all, until overload computer ... this problem is gone, but disabling the viduha remained, who faced, help please