100 hours into playing, it now refuses to launch. I've followed all suggested procedures, nothing helps. All the other gog games I have play just fine.

Try applying the Rebuild patch. It's a pretty good fix up of most major files:

https://neverwintervault.org/patch/nwn1/english/nwn-sou-hotu

Beware of the autoupdates being applied by Microsoft especially on Win10 but also on earlier versions like Win7. Several venues have been reporting that some recent updates have changed their video driver. Check to make sure the driver listed in your Device Manager is the latest one for your vcard. It's possible MS installed theirs without you noticing.

I tried that, it had zero effect, but thanks my video driver is exactly the same. here is the message i get when trying to launch attached screenshot:

That's good that your driver has not been overridden. At least that much is reliable.

Try reinstalling directly off your main drive (usually C:) like C:\GOG Galaxy\Games... etc. Players have often had problems running NWN when installed in the x86 directory, especially on newer OS (XP and newer).

BTW, as a side check, what version of DirectX is NWN running on from your machine?

1- Which operating system are you using?
2- Are you using GOG Galaxy or not?

Please remember to provide these everytime you ask a question :)

Anywho, do what Chipster suggested.

1. Backup your saves.
2. Uninstall NWN
3. Delete the NWN folder in program files..GOG Galaxy.
4. Open GOG Galaxy (I am assuming you are using it because of the ss you provided) Change the installation folder from settings which you can access by clicking the GOG icon on top left.
5. Install NWN again.

Try to run the game again and see if it works this time.

If it doesnt. Close Galaxy and go directly to the nwn directory and run nwmain.exe . Ofcourse you can try that even before uninstalling.

One other thing. Reinstall OLD directX versions that old games depend on:
https://www.microsoft.com/en-us/download/details.aspx?id=8109

That should be the link to the distributed version, instead of the web check that might just do a version check and say you are up to date.