What was wrong with the Processor?
Powered the system up last Friday and no display. Was working lovely for a week or so. Everything on defaults, just no boot. I initially thought it was the motherboard, so ordered a new one. Unfortunately that was the same. Ordered a new CPU 3700x and dropped that in the board and it worked straight away. I tried the 3900X again and no boot.
Really weird. I have never had a CPU fail in all my years of upgrades, PC Builds etc.