it has become Unallocated Space now. Do the following and create a new partition:
Click the "Start" button, right-click "Computer" and choose "Manage."
Click "Disk Management" from the left pane of the Computer Management window to access drive management tools.
Right-click "Unallocated Space" from the graphical hard drive display and select "New Simple Volume."
Click "Next" three times until you get to the formatting screen. By default, NTFS is selected. Click "Next" to allocate the space to a new partition and format it.