I use an iMac (2015) with OS X El Capitan (10.11.6), which has always worked fine with my HP Photosmart C5180. It has now stopped seeing the printer. I have tried changing USB ports on hub, and also plugging straight into my iMac. I have tried re-booting both machines, and i have also purchased a new printer USB cable. I have also tried re-setting Printers and re-loading....nothing. Any other ideas would be much appreciated?