What graphics card make/model ?, benchmark app/settings ?
Power-color Rx 480 8g
Unigine heaven benchmark 1080p starting from medium to high settings.
Furmark gpu benchmark low settings.
It runs both benchmarks for 5 seconds and immediately shuts down then I
have to restart all over again.
Where are you getting the temperature readings from?
Attach a screen shot of the Radeon Settings if possible.
Is your power supply a VS550 or a VS450?
Power color makes the RX480 8G with three fans and one with two fans, which one are you using?