I bought a external hard drive and plugged this into the mac to create a back up using time machine. (I don't really know how to use time machine but it did everything automatically and quickly). I then tried plugging the hard drive into a Windows computer and it was not able to recognise that I had even plugged the hard drive in. I have removed all the files from the hard drive and put them back onto the MacBook. The hard drive is completely empty however time machine has formatted the hard drive in such a way that I still cant plug it into a windows computer. I want to re-set the hard drive so that I can manually add the files I need so that I am able to work between windows and my MacBook. Please can somebody advise on the quickest way to re-set the hard drive.....there's nothing on the hard drive at the moment.