Hi Dodger.....Completely going back to 'square one' is in my opinion a last resort measure.
Only last week I took a laptop back to it's original factory settings, because I wish to pass it on to relative; without it having installed any rubbish of mine. (mainly a few hundred e/mails.) However,Windows Vista then required more than two hundred 'up-dates' to be installed. A lengthty process involving some hours; plus further time over a few days to re-install programmes such as Open Office, Microsoft Security Essentials, Firefox, etc etc.
Ron.