If the hard drive has failed you'll need a replacement Sky box. I'm not sure if Sky can provide a replacement - Sky+ boxes were last manufactured in 2015/2016, but there are plenty ofused boxes available cheaply on ebay. Just look for a DRX890 or DRX 895 model as they're the most recent.
Or now might an opportunity to upgrade to Sky Q. Sky will probably be able to do you a good deal.
