I have some questions and some recommendations for you...
The original problem of the system not booting might have been temporarily compounded by moving it to a different system as a secondary or slave disk. You'll want to make sure that is not an issue 1st b4 continuing w/ trouble-shooting or testing the failed disk.
(01) Is the hard disk installed in the same computer it was running in properly before?
(02) If not, was it the Master of 1st drive on the previous system - the system where it originally failed? In other words, did it contain a boot volume? (Was it the disk that the system used to boot off of?)
(03) You said the file system is FAT. Is that FAT16 or FAT32?
(04) Does the drive have an operating system on it? If so, what operating system is it?
(05) Are you sure the jumpers are set correctly for the configuration you have it in now (slaved to your master drive)?
(06) Check to see if the drive jumpers are set for LIMITED CAPACITY? (See HERE
for more information regarding jumper settings on Seagate hard disks.)
(07) Are you using a MASTER/SLAVE configuration for your two hard drives or are you using CS (cable select)? If you are using CS, both drives must be jumpered to CS and the primary (MASTER) drive should be the LAST drive on the cable (at the end).
The drive may very well be, physically, fine. However, the best way to determine that is to...
1st, Ensure that the jumper settings are correct for its current configuration (slaved to your master hard disk or as a secondary CS disk on the primary EIDE controller) and...
2nd, run diagnostics on a hard disk using boot media rather than from w/in an operating system. This is a much more reliable and thorough means of testing your hard disk.
I recommend that, once you've determined that your jumper configuration are correct (for BOTH hard disks), you run Seagate's boot diagnostics (Seagate Utilities) to test the hard drive.
(07) Do you have any data that needs to be recovered off of this drive? If so, let us know and we'll help you to recover it.
(08) If not, you can use the Seatools diagnostics to write zeros to the drive effectively erasing it and along w/ any corruption. This will allow for a more thorough surface test, too as the diagnostics will test the surface while writing to it. (This is a last result, however. Particularly if you have an operating sytem, data, etc. that you'd like to preserve.)
Please, let us know if this response was helpful for you or, of course, if you have any further questions.