Install Windows 7
Having completed the prep work, you can safely begin the Windows 7 repair installation. You'll need a Windows 7 installation disc that matches the version of Windows already installed on your system, and you'll need at least 10GB of free space on the drive where you intend to install the new version. The installation media must be able to deploy a clean Windows installation, which means that custom recovery discs from your system manufacturer or another OEM probably won't work.
To begin the repair installation process, insert the installation media and run Setup (if it doesn't launch automatically). In the Setup window, click the Install Now button, and you'll have the choice of continuing the installation with downloadable updates or without them. If your Internet connection is working, you should probably choose to download the updates, but you can choose whichever option suits your fancy. Next you must accept the terms of the license and then choose whether to perform an Upgrade installation or a Custom installation. You're repairing a corrupt install, so choose Upgrade (the Custom option won't save your personal files or settings).
After you've selected the Upgrade option, the installer will perform a compatibility check; your system should pass with flying colors, since you were already running the same version of Windows 7, but double-check to confirm that there aren't any red flags. Once the compatibility check is done, press the big Next button, and the Upgrade/Repair installation process will begin.
If the Upgrade option is unavailable for some reason, you can still perform a repair by using a simple workaround: Right-click the Setup file before you run it, and select the Properties menu. From there, navigate to the Compatibility tab, and check Run this program in compatibility mode for:. Then select Windows Vista (Service Pack 2) from the drop-down menu. Be sure to also check the box at the bottom labeled Run this program as an administrator; then click OK. Run the Setup utility again, and the upgrade installation option should be available.
The next few stages of the repair process don't require any user intervention. The installer will gather information about your system, copy the necessary installation files, and then move any personal files or programs over to the fresh version of Windows 7. This process isn't especially fast (a typical repair install took about 40 minutes on our test machine), but the amount of time required will vary from system to system depending on how much data needs to be transferred from one Windows 7 installation to the other.
Though most of the data and programs installed on your original copy of Windows 7 should make the move the new copy, a few things (such as custom themes and sounds) will not. You'll have to reinstall those after completing the fresh install.
Clean Up After the Windows 7 Install
Once the upgrade installation process is complete, you'll be prompted to activate your fresh install and answer a few basic setup questions (time and date, network settings, and so forth). At the end of this setup process Windows, will assess your machine's performance to generate an appropriate Windows Experience Index rating, and then perform a few final updates and repairs to complete the installation. Once the entire installation process is complete, you should poke around in your new version of Windows 7 to verify that all of your files are intact and all of your applications are working properly. Run Windows Update to ensure that your fresh copy of Windows 7 is entirely up to date.
To wrap up the installation process, you need to clear out the old junk data left over from your corrupted version of Windows 7. Windows will store this data in two system folders, labeled $INPLACE.~TR and $WINDOWS.~Q. If everything is working properly, you can delete these two folders, along with some other archived data. Follow the steps we outlined earlier to perform a disk cleanup, select Clean up system files, delete the two folders, and you're done. Congratulations, you've successfully brought your Windows 7 PC back from the brink of corruption! Make sure to keep this guide handy, in case you ever need to repair a corrupted copy of Windows 7 again.