To get to the following option press F8 repeatedly during startup (it'll catch it sometime between the POST and Windows loading.
1. Try booting into safe mode.
If that succeeds, let us know. If you continue to have problems:
2. If you have a Windows CD, try using the recovery console by booting from the CD and pushing R when prompted to.
Giving the hard drive external power would accomplish nothing since the hard drive won't keep the rest of the computer on. The system would still get restarted by Windows.
What exactly were you doing when the computer froze? Anything in particular? Was there anything strange? Any error messages? How long was it frozen before you unplugged it? What are your full system specs? Provide as much information as possible, makes this easier.