Grats! I was starting to think that maybe you did indeed have a stuck power switch on the front of the case (since holding the button for five seconds is the signal to shut down for a modern PSU). And GBurg's right - that's pretty much the first step for the job. Successfully replace something without shorting out everything in site and lighting it on fire.
I wanna thank all who gave the old man suggestions (on and offline). Plugged her into the monitor, etc. and she's running fine .. so far.
dracnal, was that pre or post Carly?