Thanks for the replys all - but I just checked the back of the pc and the monitor plug for some bizzare reason wasn't plugged in properly. I plugged it in, moved the box to the left a bit, booted up - all working like normal. Moved box an inch back to its usual spot, green. Inch to the left again, all working.
Basically if I move the tower a inch back to where it was the screens all buggered but if I leave it where it is, its fine. Faulty connection? Its working fine right now anyway, apart from the towers not lined up!