You need to un-install everything given from xampp previous installation. And why is there an Apache folder in the
c:\ drive? Everything controlled by
xampp will reside on
c:\xampp directory. It contains
mysql, php, ftp, apache and the entire bundle of software in
Delete everything with the
apache un-install tool first. If its not found, do it manually, make sure apache is turned off so you don't get permission error when deleting. Then clear your path vars relating to apache and other
xampp software components.
Also run xampp un-install program, it will clean up your previous installation residue including settings. (Double check the
c:\ folder and make sure there isn't any xampp folder, if any delete before the new installation)
You don't need to reboot your pc. Run the xampp installer again, you should be good to go considering you've un-installed previous stand alone Apache installation and xampp un-install and none of the folders live on the
c:\ drive and cleared your settings before the new installation.