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My Dell computer had Windows 7 pre-installed when I purchased it last year.  I recently installed Windows 10, decided I didn't like it and tried to revert to Windows 7 within the 30 day trial period. Unfortunately in an effort to resolve issues I had running Windows 10, I ran an AVG PC Tune-Up which may have deleted the files that I needed to restore as part of the trial and I couldn't revert back. I re-installed Windows 7 using the supplied CD, and downloaded all the drivers for my computer using the Service Tag recommended drivers from the website.  The initial Windows 7 install appears to work, but when I try to install the first of the drivers (Dell Update Package), it crashes with a message "The update installer operation is unsuccessful", and a view installation log link (which I can't understand). I now have several versions of the windows.old folder on my computer, and I can't delete the later ones due to "permission" errors.  I thought I was installing Windows as an Administrator? Obviously all my files/programs were wiped during the re-install, but any suggestions on what I'm doing wrong would be welcome? 
Help with re-installation of Windows 7 from CD