Sick Quicksilver!!

Resetting the CUDA should have fixed it. My QS does this from time to time..

Do you have any extra hardware installed? This happens to me after a power outage, and removing the usb card I have and letting it boot up and then reinstalling the card works everytime.

Generally, if not always, caused by the PMU freaking out.

What I've done to fix this in the past (and this is with Quicksilvers that wouldn't boot at all with identical symptoms):

1. Unplug the computer from the wall.
2. Press the power button to get rid of any residual charge (it should glow for a second).
3. Open it up and pull the battery.
4. Press the CUDA reset button, just for the heck of it.
5. Let it sit for a few minutes (just a minute was fine in my case, although I've heard up to half an hour recommended).
6. Put everything back together, start up and reset the PRAM, and hope it works.
7. For good measure, you can also boot into Open Firmware (command-option-O-F) and do a "reset-nvram" and "reset-all", which might help, too.

It's worth a shot, anyway.

The quicksilver has some power management issues. But I don't know what the problem is.