This should all be done through DOS - don't try it through Windows. If you haven't already got a bootable floppy disk with the FDISK program on it, you can download one from click here. When that's downloaded, insert a blank floppy and run it. Whne the floppy has been written, you can boot from it. When it boots, it will go to the DOS prompt. From there, you can type FDISK to run the Fixed Disk program. Then it's a case of deleting all partitions on the drive you want to format and creating a single primary partition on it. Then restart the machine with the bootdisk and format the drive with the FORMAT (drive letter) command. It's also a good idea to unplug any hard drives you don't want to format while you do this to stop you accidentally wiping data you need to keep.