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There are different ways to reinstall Windows. Which is appropriate depends on the problem you're attempting to solve.

It's time to reinstall Windows. Things are flaky, the machine's crashing every once in a while ... I just know it's time. How do I do that and still preserve as much of what's set up on the machine already? How do I reinstall Windows without losing all my installed programs and data?

There are definitely scenarios where a reinstallation of Windows is required. Be it simple "software rot" (the degradation of your system as you add, and remove, programs over time), or something more malicious like a virus or an accumulation of spyware.

The first question isn't really "how?", it's "how much?"

The first decision to make, really, is how much of a reinstallation you want to perform. Do you want to reinstall only Windows? Or perhaps the rest of the system as well?

It sounds like a lot of work ... and it is. But in my experience a completely clean reinstallation of Windows and all applications is the only real way to ensure that the machine is truly and absolutely clean.

It's a long process that begins with backing up all your data, and the installing Windows from scratch, including a reformat of the hard disk, and then reinstalling all of your applications and restoring your data.

Did I mention it's a lot of work?

"... in my experience a completely clean reinstallation of Windows and all applications is the only real way to ensure that the machine is truly and absolutely clean."

It's very close to what happens when you get a new machine. In fact, quite often, I'll time it so that it happens when I get a new machine. The new machine gets built out with all my applications and my data gets moved, and then I reformat and reinstall Windows on the old machine, but then use it for some other purpose.

So what if you don't want to go through all that hassle? Then you want what's commonly called a "repair install". When you boot from the Windows Installation CD, it's one of the options along the way. It will reinstall Windows while preserving your applications and data.

The "problem", if you want to call it that, with a repair installation, is that it does not fix nearly as many problems as a complete reinstall. If the problem is with an application, a repair install of only Windows may not fix the application's issues.

This excellent article by Microsoft MVP Michael Stevens, How to Perform a Windows XP Repair Install covers many of the issues, and the steps, in detail.

Article C2499 - December 22, 2005 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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10 Comments
michael horowitz
December 22, 2005 6:20 PM

Another option is a disk image backup.

Programs such as Ghost, True Image, Drive Image and many others make "image" backups of an entire hard disk. Doing this every month or two provides a recent synch point (so to speak) that you can fall back to when your computer starts acting up. Restoring an "image" backup is much faster and easier than re-installing Windows and your applications.

The down side is that the software costs money, and it takes time, effort and a lot of storage space for the backups.

Also, a restore will wipe out all your data files so you either have to (a) be diligent about backing up your important files or (b) keep your data files in a separate partition from Windows and your applications.

michael
January 12, 2006 11:28 AM

can i reinstall windows application with dos and how.

Richard Harper
August 14, 2008 11:44 AM

I have a partitioned drive. Windows 98 is on C and Windows 2000 is on D. I used an old version of Partition Magic (on C) to partition. I can not even boot up on 98 anymore (for a long time), and Partition Magic will not start even by clicking the exe. program under 98 on C. If I do an image copy of D on another drive, reformat main drive to D and then copy image back to it, will it work as if partition was never there, or will things have been left on C that I must have for D to work by itself? I want to do a repair install on D for Windows 2000, but want to get rid of partition and reformat first and have no logical C drive since I have been using D for years anyway. D, now, must be using drivers from C for original equipment like sound card (?), or did the installation of 2000 on D move all of those drivers over on installation? Advise, please. Thanks for all your help and site. I am 72 on fixed income or would buy you a latte.

Unfortunately there's no way that I know of to reliable run a program installed on one partition in another OS (like Win98), using an OS installed on another partition. The problem is that when programs install themselves they often install additional information in the registry that is kept with the OS. Thus even if you were able to start the program while booted in Win XP, the registry information that it had installed isn't accessible.

When you install an OS, drivers are not "moved", unless perhaps you install "on top of" the old version, on the same drive. Sounds like you did not do that, so whatever was installed was new at the time of installation.

Really, the best advice I have for you is to back up everything, and then reformat and reinstall everything from scratch the way you want it.

-Leo

john ball
October 11, 2008 8:02 PM

i installed extra memory on my pc running ME after doing this I have beeunable to start my pc it starts to boot then eventually comes up with no fixed drives found and then freezes with this message how do i reinstall windows on this machine

Ravi Agrawal
December 23, 2008 11:17 PM

michael horowitz wrote:
" Programs such as Ghost, True Image, Drive Image and many others make "image" backups of an entire hard disk. Doing this every month or two provides a recent synch point (so to speak) that you can fall back to when your computer starts acting up. Restoring an "image" backup is much faster and easier than re-installing Windows and your applications.

The down side is that the software costs money, and it takes time, effort and a lot of storage space for the backups. "

I don't mean to insult the Poster but we do have an option for almost everything in Linux. Just if you are willing to experiment & give it a little time. Of course, you are saving money, right!

See below-

http://ping.windowsdream.com/

A linux flavor of copying partitions on the fly. Its free Pal.

Ravi.

Patrick Villaroya
January 16, 2009 11:17 PM

what if once i reinstall windows and it shows the lsass error? what should i do then?

Ravneel Prasad
August 13, 2009 1:49 PM

I have a Windows Xp Pro and I started up my PC this morning and it started up normally but then it said file is missing or corrupted. It says that I need to repair it. I dont have the CD anymore to repair it. Also there are alot of data that I dont want to loose. please help me

ambar celona
May 3, 2010 10:19 PM

Can an OS like Windows XP be reinstall directly from the disc image of the original completed installation?

Depends on what you mean.

Can you use an installed copy of Windows on one machine to install Windows on another? No.

Can you use a backup image made of one machine to restore back to that same machine? Absolutely. That's what backup images are for.

Can you use a backup image made of one machine to restore back to a different machine? Typically not.
Leo
04-May-2010

cathy
May 23, 2010 2:25 AM

OMG I thought it was gone. I was crying and everything. Thank God that I found this info.page from you it brought it back. Wow your amazing. Bless you! :o)

Diane Angel
January 23, 2012 5:26 PM

My son reinstalled his windows 7 program because the original program completely shut down with all his data. Once he reinstallwd the program it asked for owner name and password. He does not know it. Is the comp. garbage now. He is lost. Please help.

Computer is not garbage, no. This is simply a software problem, the computer itself is fine. If he's setting up a computer when it asks for username and password it's asking you to create a new user name and password. Then, later, to login to the new install of WIndows you would use that username and password that you specified at install time.
Leo
28-Jan-2012

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