Hey Pyros, have you made any headway with your problem? I have almost the exact same setup as you and have been recently having the same problem with my opus not powering up. I've checked everything on my system and all connections seem fine. My system just wouldn't boot up, I would just un-hook the plug to the PSU and then try it later, that would usually work. I've never had to remove the fuse but I'll try that today. The past tow days though it hasn't really worked out. The only thing I can think of as another variable is that it's been getting colder out. My Batt should be fine too so I'm pretty sure it's not that.
BTW, my ground is less than a foot away and I also have the computer case grounded at the same point with 12g wire so I don't think my ground is bad.
Any other ideas or just a faulty PSU?