Power on the machine and enter the bios.
Let it sit.
Does the keyboard lock?
I have an over 7 years old PC.
GPU:RX 480 bought it before a year because the previous died
HDD: WD 1 TB Blue. The previous is dead also.
Motherboard: GIGABYTE z68x-ud3h-b3
PSU:Thermaltake 1500 (220V)
Keyboard: Corsair K70 RGB LUX
The problem goes as follows:
1)Switch on the PC. The PC boots normally in Windows 10.
2)Do something or nothing for some minutes.
3)The GPU goes off. The keyboard locks. You cannot modify the brightness of the keys. You cannot press Alt+F4 to terminate the current application. You cannot press Ctrl+Alt+Del
4)Hard reset from the special button on the case
5)The PC plays normally for the whole day even heavy 3D games.