This article applies to Windows 7 only. Windows XP should follow instructions in the Non-destructive reinstall of Windows XP article. Windows 8 users can use the Refresh your PC feature as described in the Repair your computer in Windows 8 article.
If nothing from previous troubleshooting articles helped to get Windows 7 working properly again, there is a way to repair Windows 7 without losing all your data, documents, settings and installed programs and drivers.
It does mean that you must be able to start Windows 7 normally, not in Safe Mode. Unlike in Windows XP, you can't boot from the installation media to do a repair install.
If your computer is unable to start Windows 7 normally, follow instructions in the Data Recovery CD/USB article or see the Recover files from hard disk article (Puppy Linux, smaller download). After recovering files, you must reinstall Windows 7 and programs, then copy your documents from the backup media you used earlier. This is the hard way in case Windows 7 does not start at all.
You need your Windows 7 installation media (DVD) that came with your computer or with the Windows 7 jewel case (box) you bought from a shop. Custom slipstreamed DVD-s (for example, created with vLite) often cause errors, so do not use these.
In case your installation media does not include Windows 7 Service Pack, but you have one installed, you might need to uninstall Service Pack first by opening Control Panel, clicking Uninstall a program (in Category view) or Programs and Features (in Icons view), selecting View installed updates on the left and uninstalling an item named Windows Service Pack. Or download a ISO image with SP1 from links given later in this article.
In many cases there is no DVD included with brand new computers, these ones have a special recovery partition instead and you can run Windows Setup from there. Please read your computer's manuals thoroughly before using Recovery process provided by your computer manufacturer, as this can delete all files and settings if you are not careful!
There are also fully legitimate ISO (disc image) versions of Windows 7 available at Digital River. Make sure you download the correct edition - do not try to install Ultimate edition if you have Home Premium installed; or 64-bit edition if you have 32-bit installed. You can easily check your edition of Windows 7 using keyboard shortcut Windows Key+Pause/Break, or by right-clicking Computer in Start menu and clicking Properties.
| Windows 7 official ISO download links | ||
| Windows 7 Home Premium with SP1 | 32-bit | 64-bit |
| Windows 7 Professional with SP1 | 32-bit | 64-bit |
| Windows 7 Ultimate with SP1 | 32-bit | 64-bit |
You can burn the downloaded ISO file to a blank DVD using CDBurnerXP. If you do not have the program installed, instructions are available in this article.
You also need the license key (product key) that came with your Windows 7. And I mean the exact same license key that was used to set up Windows 7 on your computer. You cannot change license key during this process and if you do not have the correct key, you will end up with a half-baked setup process and unusable computer.
If you bought your computer with Windows 7 preinstalled, the license key sticker is on your computer case. If you have a desktop computer, it is probably on the top of the case or on the back of the case. If you have a laptop computer, the license key sticker is on the bottom.
The license key sticker always includes text "Windows 7" and its edition (Home Basic, Home Premium, Professional, Ultimate, etc).
If you bought Windows 7 from a shop, the license key is somewhere in the box or jewel case.
In case you really can't find the key, use Speccy to find out the key that was used during installation. Follow the instruction to downloand and install Speccy, then click Operating System tab on the left and write down the value for Serial Number.
A very important thing to consider before starting is to make sure you have enough free space on your hard drive. At least 14 gigabytes of free space is needed for the repair install that preserves all your data.
Read the CCleaner article for instructions on freeing up disk space. If you need to install the program first, read the Install CCleaner article.
What will change after this reinstall?
While you will not lose any documents, e-mails, settings, drivers or additional programs installed, the reinstall will revert Windows 7 to the Service Pack version on your original installation DVD. If your DVD includes no Service Pack at all, you will have no Service Pack installed.
Also, Internet Explorer will revert to version 8.
It means that you will have to reinstall the latest Service Pack, newer version of Internet Explorer and all security updates. You will not lose any settings of Internet Explorer, though.
Reinstalling Windows 7
First, insert your Windows 7 DVD while holding down Shift key on your keyboard. This will prevent AutoPlay/AutoRun from launching the Windows 7 setup program on DVD automatically.
There is a big catch in non-destructive reinstall of Windows 7. Many users have faced a failure notice during compatibility check saying: "Your current version of Windows is more recent than the version you are trying to upgrade to. Windows cannot complete the upgrade."
To prevent this message from appearing, open the Windows 7 DVD in Windows Explorer, right-click setup.exe and choose Properties.
Click Compatibility tab on top. Click to check the Run this program in compatibility mode for: box and select Windows Vista (Service Pack 2) from the list. The original Windows Vista without any Service Packs and any earlier Windows version (XP, 2000, NT) do not support upgrading to Windows 7 (and upgrading is what we will be doing here).
Click OK to close the setup.exe Properties. Then double-click the same setup.exe file to launch it.
If the compatibility check still fails, uninstall Windows 7 Service Pack as instructed in the beginning of the current article.
The User Account Control we love so dearly will pop up. Click Yes.
Install Windows window will appear. Click Install now.
In the next dialog - Get important updates for installation - click Go online to get the latest updates for installation (recommended). About 1100 kilobytes (1,1 megabytes) will be downloaded after this.
Click I accept the license terms and then click Next.
In Which type of installation do you want? dialog click Upgrade. This will preserve all your documents, settings and installed programs while reinstalling Windows 7.
If no problems are detected during the Compatibility Check, upgrade of Windows 7 will start. This will usually take an hour or more and several automatic restarts. There is no sense in staring at the screen during the repair installation of Windows 7, so go do something else instead. 
After the lengthy process, you will finally see the Setup is preparing your computer for first use screen. This means that the process of non-destructive reinstall of Windows 7 is almost complete.
Next, you need the Windows 7 Product Key. Enter the letters and numbers and click Next. Leave the Automatically activate Windows when I'm online box checked.
If you encounter problems activating Windows 7, call your local Microsoft support line and they will be happy to provide you with a new key after you tell that you had to reinstall your genuine copy of Windows 7. Remember, this works for owners of genuine (non-pirated) copies of Windows 7 only!
In the next screen - Help protect your computer and improve Windows automatically - click Use recommended settings. This will enable Automatic Updates in Windows 7.
In Review your time and date settings, previous settings are recovered automatically, so just click Next. In the picture below are settings for Estonia, so "märts" means "March" (the month) here.
In Select your computer's current location, select the correct network type. If you are directly connected to the Internet via some modem, router or dial-up and you have no home network sharing printers or files with other computers, click Public network here. If you do share files or printers with other computers at your home, click Home network instead.
And after this, familiar Welcome Screen will appear. It will take a few minutes until all settings are applied. Just stand by.
You might also encounter a Microsoft .NET Framework repair message. The repair can take around ten minutes and it will require a reboot. Let it finish and then click Restart now. It is very likely that Windows 7 has applied some critical updates during the time already.
Now your Windows 7 non-destructive re-installation part is finished. 
But do not stop here yet! You still need to update Windows 7 to the latest Service Pack and install all other updates.
The next very important steps are:
- Install Service Packs in Windows 7
- Install EaseUS Todo Backup Free in Windows (not needed if you plan to use Windows Backup)
- Configure EaseUS Todo Backup Free in Windows or Configure automatic backup in Windows 7
Also, install free security software to be on the safe side:
