http://support.apple.com/kb/HT1492
1. Shut down your Mac if it is on.
2. Press the power button to start the computer.
3. Immediately press and hold the Command (Apple) key and one of the following:
the "s" key for single-user mode. (Command-S)
the "v" key for verbose mode. (Command-V)
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Do the Command + V. At least you will be able to see where your mac is hanging. Once you see the file it stopped on write down the error. Search for it on the web. Maybe once you have the answer, you can fix it. Sometimes booting with Command + S will bypass some errors.
Do you use Time Machine? If so, you can reboot from the install disc, and choose the Time Machine drive as your restore source.
Also read this, from
http://8help.osu.edu/1142.html
Disabling System Extensions When Starting Up in Mac OS X
Unlike earlier versions of the Mac OS, OS X does not have control panels and extensions. Therefore, it is not possible to disable extensions by holding Shift or Space Bar when starting in OS X.
However, it is possible to do a Safe Boot which allows users to boot their system into Safe Mode. Safe Booting takes longer than a normal boot and restricts what users can do after the system has restarted. However, it does three important things:
It forces the system to do a directory check at startup, hence the reason it takes longer to start up doing a Safe Boot
It loads only required kernel extensions
It runs only Apple-installed startup items
This allows users who are having system problems to start up in a relatively clean enviroment in order to identify and remove 3rd party products that may be causing problems with the system.
To perform a Safe Boot in Mac OS X:
Shut down your computer. Be sure the computer is turned off.
Press the power button to turn on the computer.
After you hear the startup chime, press and hold the Shift key on your keyboard.
Release the Shift key when you see the startup screen with the Apple logo and the progress indicator. During the startup, you will see "Safe Boot" on the Mac OS X startup screen.
To get out of the Safe Boot, restart your computer without holding down any additional keys.
PS - I hope you were not copying files from a Hackintosh, I have seen that cause hangups like the kind you are talking about.