MacPro cant see Seagate 500 gig anymore see tools wont work either

Question

Ok my 2008 Mac Pro all of a sudden wont see my 500 gig seagate hard drive anymore. I tried putting it in different bays and nothing, tried booting into the seatools ISO and its locked up and cant do anything. I even tried putting the HD in a external usb case and booted it up in both a Mac Pro, Macbook Pro and a PC and nothing.
Is this a sign that the HD is dead or possible something i can do to it to get it back up and running. Not a lot of info on it but i would like some graphic files back for some work i do.
Its a seagate Barracuda 7200.11 500gig ST3500320AS
So im guessing its the HD but anyone come across this that came up with a fix? sounds like the HD spins and no odd sounds on it.

Answer 1

if i now read your story right have you tried putting your SSD as main HDD in laptop instead of into caddy? do that and see if it loads up fine if it does not still then it sounds like either SSD is about to die so it's acting up causing it to not being regonized on your MSI but appearing fine on other laptops so try runing hard disk sentinel tool for actuall SSD health and preformance % and what i understood right is that Seagate is rubbish company since their plain hdd can easly get aprox 70% health within 36 months usage :/ so i wouldnt be suprised it's worse on SSD of theirs, so if you find health is critical then don't even bother buying a seagate again, by a Corsair or any other quality SSD instead.