GPU hard crash and black screen

[Amin7]

my rig :

cpu core i5 4590

motherboard asus h81 plus

ram 12g 1600 ddr3

gpu msi rx570 8g

psu 650 gold 

 

sorry for my bad English my pc was running fine until i had to change my monitors for while and because it was old i used hdmi to vga adapter and also i had some experment with afterburner and overclocking that i suspect it  may caused overheating of some components 

my guess is gpu failure but i like to know which part is gone bad so maybe i can repair it cause i cant buy new gpu right now

 

i can play for hours without any issue but this problems happens:(all crashes are hard crash and black screen need to restart manually)

 

1- when i open map in assassin's creed unity (also happens in main main menu) or im in home in froza horizen 5 and 4 and customize  gpu starts consuming more power than when playing it and starts to heating and fans ramps up and if i stay to long there its crashes (it happens in other games too)

2- when i exit games when its not underload anymore it crashes

3- when i wake my pc from sleep it crashes

4- some times after 5 min of gaming crashes and when i change power plan its doesn't crash anymore

 

I've tried ddu and clean install drivers, clean install windows ,changing ram sticks ,changing psu, going back to old drivers, underclocking and undervloting ( its helps on number4 but not others), i dont have access to other PC to try out gpu

[Bigun]

Have you tried removing the cooler and visually inspecting the heat sink compound to make sure it's still a liquid and not a powder?