Black screen after champion select (Windows 10)

Until the champion select everything works great. But after it I get a black screen and after a while (like 10-20 secs) i get the following message:

"Unable to connect to the server. Please check your network connection and attempt to reconnect to your game."

However I press retry on this message, it wont work. And when i cancel the message i get back to lol web and i could press "reconnect" to the game running atm. But it's useless because it starts all over again (black screen --> message). Whatever I do it wont show me the champions loading (the next step after Champion select) and the game wont start and this means GAME IS DODGED. I already lost 2 ranked games because of this -.-. Now am trying it only on costum games and it still never working!

I am confronting this issue since a week. I tried all possible solutions, since alot of other people having or had the same Problem. I tried reinstalling, resetting router, repair, fire walll off and alot more... And i also tried the one method that somehow worked for alot of people "pressing enter/space/delete Bottom after getting black screen". Nothing worked for me!!!

Please help me and thank you.