format c:\s and fdisk option -3
If I can butt in here...
fdisk is used to create partitions. I believe Option 3 deletes a partition. I can think of no real reason you should have to do this unless you are resizing the partition or changing a basic parameter.
Format /s formats the disk and makes it bootable.
Others here may have more info. I've gotten used to using Partition Magic to jiggle my partitions around instead of fdisk.