I found another faster way to reinstall the OS WITHOUT losing installed apps, files, folders. this done using the control pane, advanced recovery options, using an OEN os install cd. in my case I was reinstalling the OS. I suppose you cold also install a different edition as long as the OEM product key matches that edition. backing up data before starting install is optional. after install computer properties from the start menu is opened and that is where the key is entered a online activation takes place. if the wrong key is entered activation will fail. I have an ISO I burned and can always use that along with the same key to install and activate. I have used it twice so far on two desktops both preinstalled with win 7 pro. the COA if from my old win 7 pro DELL apparently brand/model does not matter as long as the edition matches. thought others might like to know this.
