cannot format HDD

I am running windows 7 Pro and i have 4 Hdds in the case, i am doing some in-house cleaning and want to format one of the drives (D) it has an OS on it and when i try to use the format function in 7 it refuses to do the job, i have also used Easeus partition master but this also refuses to execute the format.I have tried deleting the disk but this function also refuses to work.
Any ideas ???
thanks
Bill
P,S i have tried using admin privileges but it still refuses.

 

It's possible that the D: is the Active or bootable drive, Bill.

Can you post a screenshot of DiskMan so we can try to work out what's going on?

 

No the boot drive is (C) but i can boot from this drive although it has been a long time since i used it.
I tried to delete the drive to make it inactive but it will not let me do anything with it and it just seems as if i am locked out.
I am currently installing Kill Disk to see if that will work.

 

Kill disk tells me this disk is locked so i am using the "force wipe" function and that has started but it says 6 hours for the wipe.