Pretty much done everything I would suggest lol! When you say you've tried using the bare essentials what do you mean by that? Did you take the board out of the case compleatly, put it on some cardboard, then just plug in PSU, CPU + heatsink, graphics card, 1 stick of memory? (may want to try each stick individually) if so sounds like a duff board i'm afraid, possibly the CPU...but in 99.999% of the cases its the motherboard.