Vista - Upgrade to Vista Home Premium, Computer hangs on final reboot

I’m trying to upgrade to Vista Home Premium. I ran the Microsoft upgrade
assessment tool before I started the upgrade and it said everything was ok
for the upgrade. When upgrading the system goes all the way through the
install to what I believe is the final reboot of the install and then hangs.
There is no recovery from this, and due to this the install can’t finish.
Does anyone have any ideas on this problem? Also I noticed that in another
post someone stated that you couldn’t do a clean install upgrade to XP Pro
with the upgrade disc. If this is the case when does the upgrade stop you
from proceeding? I ‘m running XP Pro which I installed over XP Home a few
years ago and my install seemed to go perfectly until the end. Could this
issue cause my computer to hang on the final reboot?