terrell671: I found a solution for myself. Hopefully it works for you as well. I have GOG so I don't know if you will have any success.
1. Download and install a program like Revo Uninstaller or IObit Uninstaller so that you can delete any residual files after uninstalling Witcher 3 (download and use the programs mentioned at your own risk).
2. Save your games saves elsewhere before completely uninstalling Witcher 3.
3. Completely uninstall Witcher 3 and GOG (or Steam if you have Steam).
4. Use one of the programs recommended in step 1 to delete any residual files left over from the Witcher 3 uninstall.
5. Restart computer (not a necessary step but it might help).
6. Reinstall GOG/Steam and then install Witcher 3 via GOG/Steam. In a little more detail, I redownloaded the GOG program from gog.com and installed it. Then I used the stand alone GOG program to download and reinstall Witcher 3 (including lastest patch and DLCs). Both GOG and WItcher were installed in different file paths for some reason so take this into consideration when you reinstall. In other words, try installing GOG/Steam and Witcher 3 in different file paths if installing in the previous file path where issues originated still produces the same problems.
Hope this helps.
Will this solution work if I install W3 from a disc and install patches and DLC,s from gog.com? (in different paths of course)