Yosemite on new MacBook Pro is not recognising Seagate or Lacie external hard drives

My Lacie external drive and Seagate external drive are not being recognised by my new MacBook Pro 13" retina with OS X Yosemite 10.10.1. Initially the Lacie worked, but that has dropped out - cannot find it in disk utilites.

Lacie is recognised by my friends computer with Maverick - OS X 10.9.5. Currently downloading data and will try to reconfigure the external drive. Is Yosemite truly not acknowledging other drivers? USB memory key is fine. Lacie has been my back up for some years, also Seagate, but on older computers. Suggestions needed to resolve this please.