Such a mystery...
Well...
even coolermaster 460 known as a "crap" psu, it will enough to serve your machine..
try to reseat your gpu...
Remeber to watch the gpu temperature..
What temperature of your GPU in gaming mode..?
*AMD card with throttle back to the lowest speed if it too hot...
if your gpu temp is more than 80'c in gaming mode, than your gpu is the problem..
try to reseat it, clean heatsink from dust, the re-apply thermal paste will solve your problem..
And for the last, try to swap your psu with others, maybe you can borrow your friend's psu, and see..is it solve your problem or not..