PC boots from external HD

[Rich73Kelly]

I hope I am in the correct Forum for this discussion. HP Compaq 6200 Pro SFF upgraded from Win 7 Pro to Win 10 Pro. 1GB HD
I recently added an external HD for added storage to the PC. THAT is a 1TB Seagate in an "AirLink 101 3.5" USB 2.0 SATA Enclosure". It comes up in Windows Explorer as "Expansion Drive".
Last night, I went to reboot the PC for the first time since adding the drive and was notified there was no OS on the drive and couldn't boot off the drive. This is understandable BUT, is there a way to "slave" this external drive without having to unmount it before rebooting? The enclosure is powered has a power button to turn it off but, again, that involves going through the process of "ejecting" the drive before a reboot.
I had the enclosure open before I hooked it all up and noticed there is no little black jumper on the rear of the drive for master or slave like the older drives had for internal mounting so, that is not an option ATM.
Any assistance with this will be greatly appreciated.

[patio]

Unmount brfore rebooting or you risk losing all data...BTW you cannot run Win from an external drive...this is by design.

[BC_Programmer]

Either change the System's boot order so it checks the Hard Drive before it tries to boot from USB, or, you can use an appropriate disk partition editor to edit the partition of the external drive to mark it inactive.