How to completely wipe computer including OS

Is there a way to completely nuke everything on a computer, including all OSs? I've been trying to fix a computer but I think at this point its time to cut my losses and reinstall.

3 Answers

short answer, use DBAN (aka Darik's Boot and Nuke):

DBAN is a live CD with all the tools set up for securely wiping media. In general you boot from the LiveCD, use menus to select the disk, and perform the wipe.

Here is a tutorial:

Instead of downloading DBAN, you can do the same with any Windows Install disk. In fact I do it regularly with a Windows 7/8/8.1 ISO whichever I have.

1. Boot up into the Windows Installer.
2. On the partitioning screen, press SHIFT + F10 to bring up a command prompt.
3. Type diskpart to start the application.
4. Type list disk to bring up the connected disks.
5. The Hard Drive is often disk 0. Type select disk 0.
6. Type clean to wipe out the entire drive. Alternatively, type clean all and instead of just deleting, it will fill the drive with zeroes hence shredding the drive.

DBAN is the standard in data shredding, however, most people consider it an overkill. One pass of random data is often enough to make the data unreadable for anyone. Unless you have really confidential data and are afraid someone can sniff it, just use the diskpart's clean command.

If all you want to do is reinstall, then there's no need to erase entire drive (as proposed by Frank Thomas and user612013). You just want to ensure that there's nothing that can obviously be read on the OS partition.

If you want to erase OS partition, but preserve other partitions, just start re-installing Windows from optical disc or flash drive. On the partition selection screen there will be a Format button. Select the partition you want to install to, format it and proceed with installation. Other partitions will be preserved (including recovery partition, if you have one). This is what you usually want to do when reinstalling Windows.