fact: this harddive has worked perfectly for many days in both of my computers, now it dont work in either.
ummm... if the system works fine with no drive,
or any other drive.
just not with that drive.
and that drive does not work in any other system... I think it's reasonably fair to say that the drive is not working.
assuming that everthing works fine completly fine with other things just not the drive, then i'd guess the drive was broken.
as for what is broken in the drive, it could be anything, but I'm thinking it's likely to be a physical problem, some kind of short or blown chip...
if you have things on the drive that you need then the only thing that I can suggest is you either...
send the drive away to recovery specialists.
or
buy a drive of the exact same model from Ebay or simillar and make sure it works. then swap the controller board between the 2 disks if the problem is with the controller on the HDD then a replacement controller board will fix it.
other than that there is not a lot you can do, i think that you have sucessfully found through swap testing components that it's definitly the HDD that causes the trouble. for whatever reason.
I think if I had to go out on a limb I'd say that the control board is broken in the HDD and saps power or shorts something that is causing another device to fail and give beeps at the POST test.
having googled.
http://www.computerhope.com/beep.htm
the only constand beeps are with IBM bios's and indicate a power problem. -which ties in with what I've suggested that the electronics on the disk are likely faulty.