I’m my family’s resident IT guy. Â For some reason, Dad’s computer wouldn’t boot up past the initial Windows logo screen. Â Safe mode worked, however. Â After running tests for viruses, spyware, and general malware (there was plenty), it still didn’t boot. Â I reloaded Service Pack 3, and it still wouldn’t boot properly. Â Unplugging all the USB devices didn’t work, either. Â Then, I tried unplugging the firewire hard drive. Â And it worked.
Stupid Occam’s Razor.

I had a similar problem with my laptop and a firewire 800 pcmcia card… i have to leave it out whenever i boot up the machine! crappy windows!