I have a Mac cube with a Sonnet 1.8 Ghz processor upgrade (OS X 10.3.8), and firmware upgrade to support it. It was running fine, but one day it got "stuck" in the "spinning wheel" mode. So I shut it down (turned it off by pressing the startup light switch). When I started it back up, it wouldn't boot off the hard drive. It just came up with the question mark folder icon. So I tried booting off of a CD (first my DiskWarrior CD, and then my OS X installation disk). That wouldn't work either. It goes to the Apple bite image and the spinning circle, and then it just shows a circle with a line through it (the "not" icon). Do you have any ideas of what is wrong or how I can trouble shoot it?