If you've replaced the P/S, MB, processor and RAM, there's not much left. As far as powering it up without the case switch, just use a .1" jumper over the two pins on the MB that go to the front panel switch, that'll eliminate the case switch.
If that fails, the next step is to remove ALL of the other cards and external devices and see if you can get the basic system running. I'd even start without any disk drives, since you should at least get power and be able to talk to the BIOS.
Finally, there is a real possibility that you have a short to the case, have you pulled the MB out and powered it up on the bench?
If that fails, the next step is to remove ALL of the other cards and external devices and see if you can get the basic system running. I'd even start without any disk drives, since you should at least get power and be able to talk to the BIOS.
Finally, there is a real possibility that you have a short to the case, have you pulled the MB out and powered it up on the bench?