PC crashes to grey screen with loud buzzing

[Noremac999]

I have:
i5 4460 (not the problem, it happened with my old G3258)
VTX3D R9 270
Zalman Z3 Plus with 1 fan on the front, 1 on back and 2 on top (not sure if top ones are intake or outtake)
MSI H81M-E34
8gb HyperX RAM (1 stick)

So my PC is occasionally crashing to a greyish screen with jagged lines running through it with a very loud buzzing sound playing through my headphones. What is this amd how can I fix it?

 

[basroil]

Sounds like total failure of the system due to heat or bad power. Considering you didn't list the PSU, I'm going to say it's your PSU!