Western Digital Passport portable hard dri...

I have a brand new Western Digital ''My Passport'' Essesntial Portable Hard Drive. I started a sync to copy all my fixed disk drives to the portable. A window opened up & stayed for awhile showing the progress of the sync (this window also had a ''stop'' option), however, for some reason the window closed. The drive has been running forever (lights still flashing). I wanted to stop it by going to 'remove hardware' but when I click ''stop'' it tells me that the ''device can't be stopped right now - try stopping the device again later''. I have tried multiple times throughout the day w/same message. Is it ok to stop it thru the task manager (if it will let me) & if not ok to try that or task manager won't let me stop thru there, what else can/should I do to get it to stop? Thanks.