Reinstalling preinstalled Windows 8 without Windows DVD
 Probably this is nothing new, but I have spent almost one day to figure this out.   If you have a computer with preinstalled windows and want to do a clean install, the easies way is to go to http:// windows .microsoft.com/ en-us/ windows -8/create-reset- refresh-media  and create an installation USB pendrive.   This has the advantage, that you can create it with EFI secure boot, which is fast and secure.   Addition:  For Windows 7 you can use the following link: http://www.microsoft.com/en-us/software-recovery