Well honestly, if you made sure you are booting from the disk their shouldnt be an issue. But ophcrack can be a hit or miss. There could be something on that machine preventing it from booting. I would try the Offline NT Password & Registry Editor, or even PC Login Now. A simple google search will send you on the right path. Just repeat the steps with a different software and a different boot disk. Sorry this is causing you trouble but if you cant remember your password... lol not much in the way of options here.