Yosemite upgrade and corrupt external partitioned hard drive?

I upgraded to Yosemite and shortly afterward mybook hard drive 1.5tb fat formatted failed to work. All I was doing was playing itunes songs stored on the partitioned hard drive. I then tried to verify the drive it failed with error class 08. I then tried to repair it and it says it's not repairable.

I just took it and put in on my wifes Windows Surface machine and it mounted and allowed me to view files on both partitions from windows RT on her Surface...

What the heck is going on? Why won't it mount on my IMAC? I also have an NDAS Hard drive that has gone belly up but it won't mount on either the IMAC or windows surface machine...

What is going on here? I also have a 3TB external drive on this IMAC and I don't want it getting bit by this bug either nor do I want that to happen with the internal boot hard drive on the IMAC.

Anyone know whats going on here with yosemite and hard drives and how to resolve it?

Thanks Michael