I got one of these in my haul. It is a serious beast, but when I got it, it had no video. I pulled the lobo (there were no screws on the back, so someone had been inside it before). I found the video connector unplugged, and plugged it in to the personalliy card (it's got A/V ports, no modem). The cable is keyed, and the port is double keyed, so it fits both ways. I plugged it in with the key on the cable facing down, and that did not work, but after flipping it around, it worked! However, I could not get it to boot, nor eject the CD-ROM. Something happened, and I am back to no video, even with the cable plugged in the way I had it working. Only now, I also have no boot chime.
So, I just pulled it apart, took everything off the board, and blew it out with compressed air. I reassembled, and still nothing. I have heard unplugging and resetting the personality card works, but it did not in my case.
Now I can't seem to figure anything out. I am more proficient with new world macs, and 68ks. I seem to have skipped old world power macs for some reason. There is a reset button on the logic board, should I try and press it, see what happens? And if so, what is the procedure for that?
-digital 
This machine actually has two cables coming from that board. There is a smaller 3 or 4 wire cable in the middle of the card and another that looks like an ATA cable near the top. Did you connect both? (The upper is needed fore sure I'm not sure but the lower may be sound)
Yeah, OK I did get video by plugging in the smaller cable, which was disconnected. It was working fine, running OS 9. I then inserted my jaguar CD, and booted from it, but it crashed, and gave me a flashing ?. I tried booting from the CD, and it would not. So, I yanked the hard drive, and put jaguar on a 20gb using my B&W, making sure to do the 8gb partition thing. I put it in there, but now I am back to square one, with no video. The machine no longer chimes either. I have tried resetting the PRAM, and pressing the reset button on the board. That worked once, but has not done anything since then.
-digital
I did some fooling around with mine and found out that if the video/sound card is not in and you turn it on
1) the fan comes on immediately
2) it will not chime (oh yeah I unhooked the speakers from the board)
3) the green light does NOT come on.
But it DOES boot. (I can VNC into it.) Are you sure this is not happening to you? Have you tried pinging it or SSHing into it? The PS fan is louder than the disks on mine so I did not even hear it load.
On the other hand, a bad or missing disk does not keep the video from coming on.