El Capitan not recognizing Seagate

[sonofhurnu]

I bought a new Seagate external hard drive before loading El Capitan, and save everything. Excellent. Works perfectly. An older Seagate has many other documents that I want but it is not being recognized by my MacBook Pro now. Help please.

 

[Fishrrman]

Can you connect the OLD drive to another computer?

If so, what happens?

 

[Negritude]

Can you tell us the exact model of the old Seagate?