if windows is corrupted and repair tool wont help,
u can still install a new system without format! the old windows goes in an "old folder"
just put in the dvd and dont choose to format!!
u can do this:
boot a small OS from usb, that lets u start your pc and save your data.http://pcsupport.about.com/od/tipstricks/ht/bootusbflash.htm