I currently have three Seagate Barracudas 7200.11 1.5 TB drives in my system for media storage.
I just added a Hitachi Deskstar 2 TB drive.
Once I added the Deskstar one of my Seagate drives disappeared from Windows.
I have a WD 500 gig setup as my bootdrive
I have a Seagate 1.5 setup as my D: drive (this is the one that's showing failed in disk management)
I have the other two Seagates and the Hitachi drive setup as E: and as a spanned dynamic drive.
I have run SeaTools on the three Seagate drives and they all test as fine. They are all showing up in the BIOS too.