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But that assumes the lower sectors are the problem. You do not know what's wrong with it and the drive may not even be functioning for all you know or it may even just something simple such as a broken file making it not wanting to boot. It doesn't matter if Seagate recommends it or not, what you're suggesting is basically the same thing as replacing a non-functional engine in a car instead of even trying to fix it. It's a very case-specific solution that should be done only once you're certain it's the solution required to fix your drive. And for the record, to maintain drive health you usually don't need to low-level format it either unless it's already so broken it's probably time to buy a new one anyway as a lot of the things it does to the drive is already done automatically as part of the regular defragmentation process (something which is done by the operating system (Win 7 and up at least) automatically in the background.
The question, either way, was about installing Ubuntu on a USB stick. Then once that's done I would suggest trying to access any of the data on the drive from there and see if anything can be saved/recovered
before permanently deleting everything.