Not sure if its best keeping all this in your other project thread? I recall in the other thread something about a neckboard missing or not attached? is that still the case because obviously that will result in no image.
can't offer much helpful input on anything else as fortunately my model 2/3 stuff worked as is and so never had to do any real fault finding on them. What I will say though is I noticed these cabs are just 'loud' the fans just go full pelt with no speed control as such, my model 2 boards (daytona) got very warm.
Check your PSU for +3.3V, +5V - +12V not critical for boot - that's the first place to start
Then go onto looking for any LED activation on power up - there is a bank of around 8 I think - check them
Sounds like the boards are not booting up - poss dead CPU boards - they can be replaced with much less pain (financially) than the video boards - they are all step 2 - oh yes - check someone hasn't swapped the step 2 boards for step 1.0 or 1.5 - always worth a check in case you have these in cold
Were they running before?