It's got warranty? I'd send it in demanding a replacement or refund.
Generally, when any HD starts acting funny for whatever reason, I immediately save any data and get rid of it. It may have been fixable and working again for some time, but for how long... These days, with prices for TB sized reliable and trouble-free drives being this low > Amazon.com: WD Elements 2 TB USB 2.0 Desktop External Hard Drive: Electronics
, IMO no need to spend lots of time battling dying drives or take chances by continuing using them.