Helping people with computers... one answer at a time.

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.

Rather than reinvent the wheel here, I'll point you at a couple of very good resources out on the 'net.

Article C2499 - December 22, 2005

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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Recent Comments
10 Comments

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

Posted by: Patrick Villaroya at January 16, 2009 11:17 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

Posted by: Ravneel Prasad at August 13, 2009 1:49 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

Posted by: ambar celona at May 3, 2010 10:19 PM

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)

Posted by: cathy at May 23, 2010 2:25 AM

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
Posted by: Diane Angel at January 23, 2012 5:26 PM
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