How do I reformat and reinstall Windows?

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Summary: Sometimes the best approach to resolving an issue, be it a virus or simply software rot, is reformat and reinstall. We'll review the steps.

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"Reformat and reinstall" is the computer's equivalent of erasing the chalkboard and starting over.

And I do want to emphasize the "erasing" part.

It's conceptually very easy, but also somewhat time consuming.

And if not done with the proper preparation, you could lose absolutely everything on your computer.

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Reformatting and reinstalling is pretty much exactly what it sounds like:

• Reformatting is the process of initializing a hard disk to an empty state. This step deletes everything on your hard drive. Everything.

• Reinstalling is the process of copying Windows back on to your hard drive and reconfiguring it to your needs. It also encompasses the fact that you'll also need to reinstall all the application software you use, as well as restoring all the data you might want to continue to have available.

If you have an existing computer that you're about to reformat and reinstall, there's a very important first step:

Back Up

I don't care how - be it an image backup of the entire machine (my preference), or a careful backup of all the files and any other data that you want to keep - but you must do this before you begin. The process we're about to embark on will erase everything from your hard drive.

You'll also need all the installation media for everything you plan to install, including your original Windows installation disk and its product key.

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There are two basic approaches:

• Reformat or erase the disk, and then run Windows setup

• Just run Windows Setup, and let it reformat the disk

I'll spend most of my time on the second option, since it's all that most people need.

The first option gets complicated since you can't reformat or completely erase a hard disk that's in use - i.e. if you've booted from it. If you want to take this two-step approach then my tool of choice to erase a hard disk that's been in use is DBAN. Boot from that, erase the disk, and then boot from your Windows installation media to reinstall Windows from scratch.

As it turns out, the Windows setup program can be used to erase or format the hard disk as well; it's just not obvious where in the setup process you can do so. We'll examine it both for Windows Vista, and Windows XP, since they're quite different.

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Window Vista

Step one is to simply boot from the Windows installation DVD and eventually the Windows Vista Setup program will begin:

You'll then walk through a series of configuration pages:

• choose language and keyboard
• Install Now
• enter the product key
• accept the EULA

You'll finally come to this page:

Regardless of whether or not "Upgrade" is available to you, choose Custom.

After a few minutes of examining your system, Windows Vista Setup will then display this page:

This is where you tell Windows Setup on which drive you want Windows installed. Note that the list of drives on your system will likely be different than seen here.

Click on Drive options (advanced):

Note that several additional options are now visible.

First: Make sure to click on the drive or partition you want to erase and on which you want to install windows.

Second: click on Format.

Heed the warning: "If you format this partition, all data stored on it will be permanently deleted."

Press OK, and Windows Setup will format the hard disk partition that you've selected.

After the format is done, you're returned to the drive selection page, where you can click on Next to continue the installation.

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Window XP

Step one is to simply boot from the Windows installation CD and eventually the Windows XP Setup program will begin:

After accepting the EULA you'll be presented with a list of prior Windows installations:

We want to install a fresh copy of Windows XP, so press the Escape key (ESC).

The next screen shows us the available drives and partitions:

In order to force a reformat, we're going to delete the destination partition and recreate it.

Click on the drive that you want to install to, and press "D":

Press Enter to confirm that you want to delete the partition. Since this is a destructive operation (all information on the partition will be erased), Windows XP Setup asks again, just to be sure:

Press "L" to delete the partition.

Now you've got an unpartitioned hard disk. Windows XP Setup now presents you with the list of drives and partitions again:

Select the unpartitioned space, and type "C" to create a partition. You'll then be asked to enter the size of the new partition:

The default value should be the maximum appropriate for that partition, so simply press ENTER to continue.

Setup returns you to the partition selection screen:

This time what was the unpartitioned space is now "Partition1 [New (Raw)]". Select that and press ENTER.

Windows XP Setup notices that your destination partition is not formatted:

The default is to format using NTFS, which is just fine for more situations. Press ENTER to let the format begin.

Once the formatting is complete, Windows Setup then automatically begins copying files to the newly formatted partition and continues with additional options and selections related to how you would like your new installation to be configured.

Related:

• I don't have an installation CD for Windows XP - what if I need one? At some point you'll need your Windows installation CD. If you don't have one, you could be out of luck. Be sure to get one and keep it safe.

• Don't lose your keys! When you purchase software you're not always buying what you think.

• What's the difference between an upgrade and an upgrade? With all the different versions of Windows it's easy to get confused, particularly when the term "upgrade" can actually mean two different things.

Article C3889 - October 14, 2009