I am having problems, too: I don't remember having problems on my laptop, but I am having problems on my desktop. It looks like everything has shutdown, but the fan and lights on the box remain on. I have to hit the reset button then the power button once the bios bootsplash appears. I have a fresh install of the mini cd and did an upgrade, but that's it.
I just found a thread with a similar problem. The author also has an ati card in his desktop. His solution was to edit a file. When next I boot that machine, I will follow the instructions, and of course, report back.