Lightroom 6 unable to open DNG files

Hi, I´m using Lightroom 6. Shooting the last mont with a Nikon  D850. Because of NEF files, i downloaded Adobe DNG Convertor. After first Convert, I was able to open and edit the DNG´s in Lightroom. After second session of shooting, after I convert the new files to DNG and trying to open them in Lightroom, the Lr was starting but desapers after 20 seconds.  I tried it diffrent times also to change directores etc, but Lr was unable to run the DNG´s.

I aslo didn´t get a error massage. In the starting process, Lr just desapare.  But without trying to run the DNG´s, Lr was running perfectly. Also the first imported DNG was no issue to edit, save or whatever..

I thought, it´s a Lr issue, so I uninstalled it a installed it new. But with same negative result. To make the story short, I reinstalled the whole windows, than installed Lr. again. Than Adobes DNG converter and again. First Convert and Import was with no issue and than after that, exactly the same problem with the new DNG´s. The first Import was still there and no problem to work with. 

I don´t wan´t to upgrade to the new Lr cause it´s sadly not in my budget to pay monthly. Thats why i buyed the last CD version. And till know i was totally happy with it. I don´t know if its important, but Im using  Win10 prof. and by Lightroom is telling by checking the updateds, that theres no updated available.

Please had someone the same problem and now´s the solution for it? (PS, sorry for my english)

Thanks to every one who can help. 

J.T.