|You don't copy your disk, you clone it.|
Copying files does just that, copies files. It doesn't copy the system area that makes the disk bootable.
Cloning copies everything, every single bit so the clone is an identical copy of the original in every way.
If you go to the drive manufactures web site you should be able to download a suitable tool to do that.
Seagate has Disc Wizard which will do the job but you need at least one Seagate drive in the system for it to work.