See this shorting problem - I think mine is doing the same thing. I turn it on and it tries to start, and then I hear a few very faint cracking noises and it turns itself off. It does this 4 or 5 times on the trot, and then normally decides to boot up, and it's fine then all day. Same problem then though next morning. I thought it was the PSU that was on the way out, but perhaps I've got the symptoms of this shorting problem.
Where exactly have you been finding the wires are shorting, is it directly behind the switch? If so I assume that the front will have to come off to sort it? Normally taking these off breaks all the plastic clips etc, was this ok to come off on this case?
I was planning a new Seasonic PSU for it anyway, so may go order one. If I'm going to have to strip it down to trace a short I may as well change the PSU at the same time. Are all the Seasonic PSU's (i.e different watts) the same physical size, or are the 450w's etc bigger?