I don't think 5 seconds is unusual for it to fail, especially if the boot block is damaged.
No, floppies are not durable media. Magnetic media is not the greatest for long term storage of digital data. Especially floppies.
Maybe some types of streaming tape drives are good for long term archival storage (like DDS tapes), but not 3.5" floppies.
It *could* be your drive has failed, but I would try the weakest link first - and that would be the floppy disks themselves.
Didn't the Magic Pack you received come with *any* other bootable disks you could try?
Yes. There were some other disks in there as well, but I really don't want to risk screwing them up, in case it's the drive that's failing.
Is there no other way to check whether the floppies are broken or not? Weren't there two or three Windows tools that made it possible to read Amiga floppy disks without the need of a catweasel?
Furthermore, if the workbench disks turn out to be the culprit, is there any way to install Amiga OS 3.1 without the need of a floppy drive? I don't want to spend money on another set of WB disks. Especially if there's a fair chance these might turn out to be faulty as well.
EDIT: Found the tool I was thinking about. It's called adfread. I'll still need an Amiga floppy drive for it, of course.