Computer Taking Enough Time To Boot Up To OS?

i reinstalled my os wich is xp media centre edition, just becuse i wanted to clean up my hd sinse i have done this everything is fine and dandy except wen i boot up it takes like ages it never used to do this before, this is not a startup time problem it is a boot up time problem as in wen u boot up your computer and u have xp its a black screen with the white loading bars at the bottom this is when it takes its time, its wierd cuse wen i load up vista its fine, also i dont really have anything running at startup only explorer