Well things have got much stranger.
Tried removing the CMOS - no change.
Was getting ready to RMA it, took all the cables off (CPU fans, Power LEDs etc) - Then had to put them all back in as my 3TB drive isn't recognised in my old system and I needed to back some data up. I hadn't removed the RAM, GPU or CPU at this point just the silly cables.
Tried the bios for some reason and it worked!
It's been running fine for 4 days, slowly building up the drivers and updates, able to get into the bios, confirmed F14 was installed on it and it's still detecting everything correctly - then today it's gone back to the black screen AGAIN! I booted up and SP1 was waiting if that's possibly relevant. I'm guessing it's a driver/software based issue but I have no idea what the conflicting object could be???