System hanging

[Clearcut]

Forgive me if this is not a hardware issue but I am puzzled.
Recently I will be working away and I will suddenly hear the sound of the PC clicking off - like on a shutdown. However, all the fans are still spinning and I have a frozen image on screen. Sometimes I have been able to move the mouse for a while. I have used Rivatuner to adjust my GPU fan to a reasonable temperature so that seems cool.
Any ideas what this could be please?

 

[PhoenixUK]

Well, try running everything on default stock speeds ? Non OCed ? And that will mean the GPU fan on default as well.

Sounds like either GPU or HDD prob to me.

 

[Clearcut]

Thanks, I was leaning towards HDD too.