check the cables to see that they connected. also see with your hand the drive is spinning. also try using seatools to see if it sees the drive. some seagates had firmware issues and would brick themselves.
used Seatools myself for my 2nd drive that suddenly disappeared from My Computer. Only my boot drive comes up.
My 2nd HDD is recognized and passes all test in Seatools. Cant see the HDD in the My Computer section coming up though. Any idea how I can get access back to all my files?