Setting or removing the jumper switches at the rear of the unit is used to determine slave (normally no jumpers set) or master (positions vary in settings).
Another possibility is that your BIOS is not set up to recognise the additional drive.
Samsung Galaxy S8 review
1995-2015: How technology has changed the world in 20 years
What’s happening in VR right now: From psychedelic art to combat therapy
Siri not working? Try these troubleshooting fixes
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.