What is the problem after you move your prestashop installation from subfolder to root / main folder ? You got infinite redirect loop and now it looks like johndoe.com/subfolder/subfolder/subfolder... and so on
The solution is simple actually, please check that you have already done this two things :
1.Change base url. from /subfolder into / (for root or main folder), you could find the base url in your prestashop configuration file.
2. Delete htaccess and regenerate new one after you change your base url configuration.
Its all done, and you could see your prestashop installation on your main folder / root domain now.