Reformatting

Alright, if anyone could help me out it'd be great. I've already backed everything up, checked it all twice, and am ready to format. So i put in the boot disks, let it all load, and as i type - format C: (or format C: /fs:ntfs) and it says "Not able to format," or something of the like. Basically it won't let me format. Anyone have a solution? yes im absolutely sure i am going to reformat, don't try to talk me out of it