It's alive, IT'S ALIVE!
So, yeah, got it sorted and it's working well. Ocuk replaced my motherboard very quickly (props to them, really sorted me out. Communication was not brilliant, but I got my board fast) and it worked first time.
The motherboard failure did corrupt my OS drive, so I needed to re-install. Also, randomly one of the SATA cables no longer works... But, everything seems fine now. I can't help but think that the problem may have started with the power supply, but I guess i'll never know now.
If Ocuk are reading, your prompt service was the difference between keeping me as a loyal customer and losing me. Thank you for replacing the board quickly, I have my eye on a new video card, either a 980Ti or 390x. When they are released I’ll be sure to place the order here.