I wrecked the motherboard of my previous desktop computer, but the 500GB hard drive was perfectly good; plus, it contained all my files. So I installed it into my current desktop computer. It still had Windows and some Windows-oriented folders, which contained system-protected files that I could not erase -- even though Windows no longer uses any files on this second hard drive.
I knew I could get Linux to erase the folders and files, but I didn't want to turn my desktop computer into a dual-boot machine. I tried running Linux in a virtual machine using Oracle VM VirtualBox software, but I couldn't access the drive.
So here is my solution. I had wanted anyhow to install Linux Mint 15 on a spare, external, USB-powered drive, so that I wouldn't have to deal with dual-booting on any computer. I did that (using a utility called YUMI), and then attached the drive to a USB port on my desktop computer.
As my Acer desktop computer was booting, I pressed F12 repeatedly to access the boot screen. I selected the external USB drive, and booted into Linux. I was then able to easily erase the Windows folder, and other folders that Windows wouldn't erase.
The effort freed up 38GB of disk space.
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I have found the best way to deal with an old Windows hard drives is with a Mac. The Mac's Disk Utility program (found in Applications > Utilities) effortlessly wipes out existing partitions and reformats drives in seconds. Windows own disk utility is wonky about partitions, and Linux is too technical.
(Hard drives pulled from Windows computers usually have three partions, two of which are used for backup and OS recovery purposes. You gain disk space by removing these partitions, which become unecessary when the drive no longer runs Windows.)
Mac OS X does not, however, support NTFS natively, and so you'll need to install a driver to recognize NTFS drives and to format them. I use the free NTFS-Free driver from Anton Altaparmakov. (Some others say they are free, but don't tell you they are free for just 15 days.)