How to initialize my external hard drive it is write protected

Try this:

Go into Device Manager.
Right-click the external drive & choose "Properties".
Click the "Driver" tab.
Click the "Uninstall" button.

Unplug the drive from USB port.
Restart Windows.
When Windows has fully loaded, plug the drive back in.
 
I tried this and it worked, in Windows 7. Start Cmd.exe as administrator, then:

C:\> Diskpart

DISKPART> list disk
DISKPART> select disk (id)
DISKPART> online disk (if the disk is not online)
DISKPART> attributes disk clear readonly

Then I was able to manipulate the volume in Disk Management control panel.