I have installed Win 10 with some problems but most of it is settling down now. I noticed that my FreeAgent desktop external drive is not recognized by the system. My original 2008 was replaced in 2012 with model ST305004FDAIEI-RK. I don't find this model# on the Win10 compatibility list but there are some very similar.
I downloaded the Seagate software but when I run the program it tells me that no external drive has been located. There is no device driver and I don't know how to get one. Any suggestions on what to do next. ETA - I just realized that this is the #$%# paid version of the software, which Seagate at some point started doing. The backup software used to be included with the purchase of their external drives. So while this DOES work, after a month you'll have to ba $60 for it. There are less expensive options out there if you're going to have to pay for the software anyway.
I can also confirm that the software Steven linked is working for me. I've had a 1Tb FreeAgent Drive that I've used for generation backup of development files and some personal data for years.
Seagate Manager just stopped working, because it could no longer see the drive after Windows 10, even though Windows 10 sees it fine. The Windows 10 backup system does work, but I was unsatisfied with my control over what was happening, and for some reason it was sometimes missing current file, and seems to ignore 'backup now' instructions sometimes. Make sure to Download the install labeled as he suggested. The 'top' selection in that download section looks like backup software, but is actually just a driver you don't need. The bottom choice is the correct one. I have it installed and performing a backup as I type this.