format your computer via your hdd
the limitation is that u should have a OS previously installed and u can't format c drive except from it u can format all other drives
make a image of your xp sp2 in your hdd or borrow it from someone in your pen drive and mount this image via demon tool,alchohal, clone cd or any other virtual drive
now double click it
a windows appears and ask u what do u want to do
select install windows xp professional/home edition
now a new windows open in that click next and it will ask for key
give the key
click next
now a option comes copy files in here click copy files in hard disk
now press next
it will start copying file in your hdd
and restart the windows
now follow the normal procedure
and now u can format your any drive (if it has OS also u can format)