Hi guys.
im new to this forum and already with a big issue on my hands and appreciate any help,

my model is:
Seagate ST2000DM001 2TB
PN: 1E6164-570
FW: CC45

basically this stemms from the external usb 3 hard drive here: http://www.amazon.de/gp/product/B00JV1Y ... 1_49284081

This external HDD was used as a big music and movies library connected always to the pc.
at first the problem was that from time to time the HDD used to simply become unrecognized while connected to the pc, which required me to unplug and plug again the usb/ power supply so it becomes recognized by the pc.

one day it stopped being recognized all together. and when i plug it in, it makes the usb connected noise. then spins. and then makes the usb disconnected noise and the blue led flashes on and off and then it spins slowly for eternity

i know its not reccomended but i've opened it in a clean environment. and witnessed that the arm at 1st jitters slightly and then stays at one spot while the disk spins. perhaps this is normal, im not sure.
There are no bad sounds coming out of the drive or anything like that.

of course the HDD been tested with multiple PC's and is not recognized in bios nor device manager. i've been told that this might be a hardware issue. but my limited knowledge tells me it might be the PCB? it has been inspected with naked eye and no burned parts were observed..
please suggest how do i continue from here

It's not anything related to the PCB, so don't even attempt that or you'll just be complicating the situation. The drive almost certainly has an issue with the auto-reallocation and/or media cache. Opening it and running with the top cover off was a bad move that probably already destroyed a lot of data.

To get the data back will require a PC-3000, so unless you're looking to spend $10,000 you'll need to bring it to a pro.

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Data Medics - Hard Drive, SSD, and RAID Data Recovery Service Company

exactly, you have open the hard drive totally un-necessary.
if data is important send it to a Pro.

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Data Recovery Pakistan

opening the HDD although it's not necessary, but it doesn't concerns me, since it has been opened in a clean environment as the OP mentioned:

but running it with the lid open...