Looking at your screenshots there is some oddities there. For the general folder hierarchy for ST3 (including MP2) and ST4, please have a look at:
https://www.ikmultimedia.com/faq/index.php?category=11&topic=sampletank-4 then click on "I can't find or load my Virtual Instrument's sound content library, what can I do?".
In the first screenshot, I would expect to see only 2 folders at the second level - "SampleTank 3" and SampleTank 4". The disk path in ST3's (or MP2's or Syntronik's) Settings should be to "IK Multimedia/SampleTank 3" - the software is expecting to see an "Instruments" sub-folder (and other stuff) within the disk path.
The Sound Contents paths in ST4's Settings should be to "IK Multimedia/SampleTank 4" and to "IK Multimedia/SampleTank 3".
Here is the folder hierarchy here, in Windows 7 (I do not have MP2 or the full Syntronik):
>>>
https://i.imgur.com/PTDuBqC.pngOnly do the following if you fully understand what you are doing. -- It looks like the other folders and files at the second level are the result of some earlier installation or move.
-- Look in the other folders at the second level and compare that contents with that of the same folders in "IK Multimedia/SampleTank 3"
-- if the second-level folders have different or newer content, move it into the equivalent folders in "IK Multimedia/SampleTank 3".
-- Rename those other folders at the second level only, just to keep them out of the way; add a suffix, say, "_notused".
-- Rename the cache.db files at the second level only, just to keep them out of the way; add a suffix, say, "_notused".
-- Start MP2 standalone, and set the disk path to "IK Multimedia/SampleTank 3" and let the database rebuild. Close it.
-- Start Syntronik standalone, and set the disk path to "IK Multimedia/SampleTank 3" and let the database rebuild. Close it.
-- Start ST3 standalone, and set the disk path to "IK Multimedia/SampleTank 3" and let the database rebuild. Close it.
-- Start ST4 standalone, and set the disk paths to "IK Multimedia/SampleTank 4" and to "IK Multimedia/SampleTank 3" and let the database rebuild. Close it.
Phew. If you do try this, please report back.
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I don't think that reinstalling the software would help. Reinstalling the sounds libraries would - that is simpler than the above steps but will take longer.
But if you do decide to reinstall, please reply to Support, with your screenshots or a link to this thread and ask for precise step-by-step instructions.