From my experience with a Quadra 950, it's a typical dead PRAM battery syndrome and pushing both the reset and interrupt buttons simultaneously had nothing to do with it. I had to get the timing right between twisting the key from 'on' to 'off' and back to 'on' position to get it to show the video output and start up normally, instead of just switching on the internal fan.
This will take a couple of tries, trust me. And when I say
couple, I mean something like 40-50 times. Quadra 950 seems to be real picky about that, unlike other old Macs with dead batteries.
Just make sure you connect your screen to the onboard video first. I don't know if it makes a difference, but it might.
In my case a brand new battery made the problem go away instantly and now it runs happily with 3 SuperMac video cards inside
Good luck with your Quadra. It's probably the coolest Mac made up to date.