It is definitely good practice to zap the PRAM after doing just about anything under the lid, even just changing the battery. And sometimes once wont fix it but twice will. Go figure lol. And a cuda reset is what i consider the first step to troubleshooting any failure to power on properly... make sure to do this with the power unplugged. that said it sounds like you may have some more sinister problems at play here.
I did notice you said one of the cards has ADC only correct? If so, this card may require additional power from somewhere, as ADC monitors are powered off the card itself, which in turn must get I beleive it is 28V (dont quote me on this figure however) from somewhere or another. Apple fed in this seperate voltage line through a pin on the AGP port in the G4 and G5 which came standard with the ADC port, when all Apple displays used this inteface. However given that PCI does not have this power feed as far as I am aware, it must come from elsewhere... unless the card has some kind of step-up circuit onboard. This would presumably require some rather bulky analogue componentry on the card however so I dont know if this would have been how it was done, or whether the card would have required some external power supply for the display port. In any case, given the wierdness of ADC, i would do some research into the workings of that specific card before writing it off. As for the Rage that is harder to diagnose.
Out of curiosity, what is the model number of the HP monitor and what size is it?
I did notice you said one of the cards has ADC only correct? If so, this card may require additional power from somewhere, as ADC monitors are powered off the card itself, which in turn must get I beleive it is 28V (dont quote me on this figure however) from somewhere or another. Apple fed in this seperate voltage line through a pin on the AGP port in the G4 and G5 which came standard with the ADC port, when all Apple displays used this inteface. However given that PCI does not have this power feed as far as I am aware, it must come from elsewhere... unless the card has some kind of step-up circuit onboard. This would presumably require some rather bulky analogue componentry on the card however so I dont know if this would have been how it was done, or whether the card would have required some external power supply for the display port. In any case, given the wierdness of ADC, i would do some research into the workings of that specific card before writing it off. As for the Rage that is harder to diagnose.
Out of curiosity, what is the model number of the HP monitor and what size is it?