What amiga are you trying to use it with?
Is your PSU struggling maybe?
Have you tried a shorter cable?
Absolutely certain that jumpers are okay?
Or maybe that drive doesn't like PIO modes...far fetched but who knows.
Or maybe there's a bad block where the amiga is trying to write the partition data/RDB.
http://en.wikipedia.org/wiki/Amiga_Rigid_Disk_BlockI know years ago I used to download the Seagate hard drive diagnostic tools and run tests on my Seagate drives. That's all I can think of right now.
Take a look at this though:
http://aminet.net/package/disk/misc/fat95In the C folder in this archive there's a command called "dd". With this command you can copy blocks from one hard drive to another, from one hard drive to a file, from a file to a hard drive etc etc. It's very easy to use and the instructions are in the English folder within the fat95 instructions.
You can copy any hard drive/backup anything with this little command. Because it bypasses the filesystem and doesn't care what the drive is, I thought you could use it to test your Seagate by writing data to it from a file, particularly the first few blocks. Infact, if you connect your 80gig and your existing hard drive together, then you could do a direct copy from your old drive to your new 80gig one and once it has finished (may take a while depending on size of your existing drive) turn it off, make the 80gig master and see if she boots. Just be careful though to not get mixed up with unit numbers and thus erasing/modifying the wrong drive. Units numbers start from 0.
I have also used another a tool that gave device information which maybe helpful, but I can't think what that is called now but I may be able to find it tomorrow. It just may well be this though:
http://m68k.aminet.net/package/disk/misc/SCSIQuery