Hanscraft, the 8 boot thing is rather annoying. As soon as you see it boot up, at the "Touch the Future of Reading" screen, immediately hold down your power button. However, it doesn't immediately power down, so keep your finger down for awhile longer. I learned to watch for a second flicker, but if you just hold it down, like Kryto said, for another 15-20 seconds it will completely shut down. When you get to the 9th reboot it will automatically switch to the screen with the green arrow that says something like "installing new file" so you don't have to worry if you end up losing count.
See the link SCION linked to above.
Then, when you're ready to try rooting the machine again, try using these instructions. I found that the screenshots helped me a lot over just the text instructions.