I installed 10.5.5 on my hackintosh, but it crashed, and I had to hold the power key down to shutdown and then restart.
On restart I got the message "You Need to restart your computer. Hold down the power button for several seconds or press the Restart button".
When you do this you get the same message all over. If you look at the top of the screen in the boot messages you'll see "Unsupported CPU \n" and "AppleIntelCPUPowerManagement".
Whats happened is that the updater has installed the kernel extension (kext) AppleIntelCPUPowerManagement.kext so you need to remove it.
To do this boot from the DVD.
On my MSI Wind / Advent 4211:
- hold down F11 on boot
- select 'boot from DVD'
after the usual whirring away you'll get the start of the installation.
- select you language. I selected English
- click 'continue' at the welcome message
- click Agree when asked
At the 'select destination screen' go to the Utilities menu and select Terminal.
When the terminal window opens type:
rm -rf AppleIntelCPUPowerManagement.kext
Quit from terminal
Quit from the installer and click restart.