Roger has a 3TB drive in his tower and it's getting full. He bought a 4 TB drive to replace it. Copied everything over. Now the drive isn't being read by Windows after he installed it into his Tower. Leo says it could be the size of the drive. But Windows 10 should be able to read it. Leo recommends trying to recopy it while it's installed in the machine. Reformat the drive and try again. Or, just keep the 4TB drive as an external drive. The speed isn't all that important. So if your PC can read it externally, and your internal drive is fine, just keep it that way.