I've just got a new Mac Mini. When I plug in and switch on the external hard drive I was previously using to back up my PC, my screen goes blank. No pressing of keys or moving of the mouse will bring up the Mac Mini again on the screen. It stays that way until I disconnect the hard drive and turn the power off to the Mac Mini. But this does not happen if I plug the hard drive into my MacBook Air. Also, I can read documents and files which are on the hard drive and drag and drop them onto the Mac Mini or the Macbook but I cannot put any files from the Mac Mini or MacBook onto the hard drive. Any thoughts anyone?