Reformat a Donated Computer’s Hardrive

Hi,

Would anyone have any suggestions on reformating a hardrive that has had security software installed. I currently have 20 that were donated for class use and FORMAT, FDISK, and reinstallation of Windows does not work. Everytime the computers either give an alert, an error message, or other non progressive responses. Some even are set to stay at a certain drive and will not go back to the root. Any suggestions other than throwing them in a dumpster would be greatly appreciated.