3TB Seagate Expansion drive does disappearing act

I couldve sworn I posted this question over a month ago but I cant find it anywhere. Not surprising, I dont remember where I parked my car. I might have posted it to airheadsЯus.com for all I know. I have several Seagate 3TB STBV3000100 Desktop Expansion drives. I realize this question might be better suited for the Seagate support forums but I get this weird message when i try to login:

Login Error, your attempt using single sign on with an identity provider certificate has failed. Please contact your salesforce.com administrator for more information.

I have absolutely no idea what any of that could possibly mean. But that is neither here or there.* Its just that I am becoming desperate and Im hoping the huge wealth of knowledge here in sevenforums might offer some assistance. The drive has been working fine for over a year (just a little longer than the warranty of course). Suddenly it disappears from the drives listed in Win 7 Pro. I have tried switching out the data and power cables and USB ports and tried this on different Win 7 computers. When it powers on the blue activity light comes on as it should and I can hear it spin up Within a couple of minutes, the light goes off and it spins down. During this period Win 7 does not see it at all. Both the data and power ports seems physically stable from what I can tell from simple observation. I have not taken it apart (yet). If anyone could offer any suggestions on what my next step should be I would be extremely appreciative. Thank you!

*I mean no disrespect by posting here instead of Segate. I opened a ticket with them regarding the login error but they have have not responded.

I sync the two 3TB drives to protect from physical drive failure. The ironic thing is this is the primary drive and had data that had not yet been synced to the backup drive which is the functioning one. Yes, when disconnected and reconnected it repeats the same behavior.