You could try running the mediator config program included on the MMCD (I think it's called mediatorconfig).
Just run it in report mode (there should be two modes iirc - "report only" and "set prefs and report" or something like) - this at least will check to see if you have all the correct libs installed.
You said you copied your original "boot" disk form backup - does this include and overwrite all you libs: and c: directories? If not, then you may be missing libraries which were on your original installation.
Btw - as alternative for anyone who finds themselves in a similar position with the power switch thing - just connect the "reset" or "turbo" switch to the "power switch" header on the mediator - hey presto, ATX switching power supply in your power tower with no need for fancy adapters.
EDIT: Why are you bothering with connnecting drives to the internal IDE connector when you have the Blizzard Scsi kit (as per your sig)? Much faster and better and supports autobooting.
