I'm caught up in so many threads I thought you had Windows 8.
Click Start > Type CMD > Right click it and Run As Administrator
Type DISKPART press OK
type LIST DISK press OK
select your disk you want to partition and type SELECT DISK 0 (example)
type CLEAN and press OK
Go back to Disk Management (Start > type Disk Management)
you should see the disk in there and it should need initialising. This can be done by clicking on it.