if you have lost partition infomation on your hard drive you may have to re-partition and format and then re-install windows have you backed up your work before hand as you may have lost it already.

Which windows are u using 95/98 ME, NT, 2000 or XP and what size is your Hard Disk?

Probably worth taking the time to sort out what u need and how you need it, OS and size of partitions u want while you do this, as you dont want to end up doing again in the future cos u run out of room or something doesnt work correctly cos of ur OS