Help!!!!

K so i was havin realy bad problems with my pc like virus wise and all sorts
and i had a copy of xp home but on my pc i had pro and i was out of options and went to installed the home edition obviously taking out the pro
and now my pc is booting up get to the xp start up screen with the little loader at the bottem the loaders goes across like 10 times then freezes
Is it just taking alot of time to load cuz it was just installed or am i lookin at a prob???
Much help from anyone would be great
thanks