Partition a hard drive

I was reading a tutorial as to partition a hard drive.It describes how to go to the
Disk Management,then right click where it indicates "unallocated space" and a
NewSimpleVolume option should open.However the problem is that
this NewSingleVolume is dimmed and nothing further can be done.
The hard disk to partition shows as Disk0

Can anybody help with this issue or explain how to partition a hard disk,using Windows 7.
Thank you

AntonABC