Recently I've gotten a R9 270. I used it for a while then one day when I turned on my computer my fans weren't spinning I wasn't sure why but I thought nothing of it. But while playing Overwatch I noticed my fps dropped (60-12), which made the game basically unplayable. When I touched my gpu I noticed it was extremely hot. So I came up with the conclusion that it because of both my fans not spinning, I've already tried looking online for a solution (Update Driver, reinstall driver, switching the pci cable)
but nothing I did worked
Test the power supply to make sure it is getting power.
Test GPU in another computer or take it to a repair shop to have it tested.