The FDisk utility is no longer supplied with recent Windows operating systems.
To reset disk partition information - boot using the install CD
and choose the install/repair option.
To do a Hard Disk reformat completely outside of Windows you can use FDISK from Windows 95, 98 or ME see Q255867
Alternatively there are many third party formatting utils such as GDISK that will do the same thing.
For more advice and other links look at FDISK.com
MSINFO - Windows Diagnostics
FORMAT - Format a disk
FSUTIL - File and Volume utilities
Dmdiag - Display disk properties: Size, Status, Type...(Win 2K ResKit)
DiskMap - Document disk structures, such as the master boot record (Win 2K ResKit)
Equivalent bash command (Linux): fdisk - Partition table manipulator for Linux