NTFS is missing, Ctrl Alt Delete to restart?

Recently plugged my 1TB External Hard Drive to a different computer. I got the message yesterday and today when trying to boot up. The first time, restarting did the trick. The 2nd time, I had to unplug the External Drive for it to go (made 2 restart attempts before this). Microsoft's article says alot of stuff about partitions, but the drive I added is connected by USB. Should I be worried about this persisting? Or just keep it unplugged when booting up?